| Oracle® Database Programmer's Guide to the Oracle Precompilers 10g Release 2 (10.2) Part Number B14354-01 |
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View PDF |
| Oracle® Database Programmer's Guide to the Oracle Precompilers 10g Release 2 (10.2) Part Number B14354-01 |
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|
View PDF |
This appendix contains the following sections:
This appendix contains descriptions of both SQL92 embedded SQL commands and directives and the Oracle embedded SQL extensions. These commands and directives are prefaced in your source code with the keywords, EXEC SQL. Rather than trying to memorize all of the SQL syntax, simply refer to this appendix, which includes the following:
A summary of embedded SQL commands and directives
A section about the command descriptions
How to read syntax diagrams
An alphabetic listing of the commands and directives
Embedded SQL commands place DDL, DML, and Transaction Control statements within a procedural language program. Embedded SQL is supported by the Oracle Precompilers. Table F-1 provides a functional summary of the embedded SQL commands and directives.
The Type column in Table F-1 is displayed in the format, source/type, where source is either SQL92 standard SQL (S) or an Oracle extension (O) and type is either an executable (E) statement or a directive (D).
Table F-1 Functional Summary of Embedded SQL Commands and Directives
| EXEC SQL Statement | Type | Purpose |
|---|---|---|
| ALLOCATE | O/E | To allocate memory for a cursor variable. |
| CLOSE | S/E | To disable a cursor, releasing the resources it holds. |
| COMMIT | S/E | To end the current transaction, making all database change permanent (optionally frees resources and disconnects from the database) |
| CONNECT | O/E | To log on to an Oracle database version 7 instance. |
| DECLARE CURSOR | S/D | To declare a cursor, associating it with a query. |
| DECLARE DATABASE | O/D | To declare an identifier for a nondefault database to be accessed in subsequent embedded SQL statements. |
| DECLARE STATEMENT | S/D | To assign a SQL variable name to a SQL statement. |
| DECLARE TABLE | O/D | To declare the table structure for semantic checking of embedded SQL statements by the Oracle Precompiler. |
| DELETE | S/E | To remove rows from a table or from a view's base table. |
| DESCRIBE | S/E | To initialize a descriptor, a structure holding host variable descriptions. |
| EXECUTE...END-EXEC | O/E | To execute an anonymous PL/SQL block. |
| EXECUTE | S/E | To execute a prepared dynamic SQL statement. |
| EXECUTE IMMEDIATE | S/E | To prepare and execute a SQL statement with no host variables. |
| FETCH | S/E | To retrieve rows selected by a query. |
| INSERT | S/E | To add rows to a table or to a view's base table. |
| OPEN | S/E | To execute the query associated with a cursor. |
| PREPARE | S/E | To parse a dynamic SQL statement. |
| ROLLBACK | S/E | To end the current transaction, discard all changes in the current transaction, and release all locks (optionally release resources and disconnect from the database). |
| SAVEPOINT | S/E | To identify a point in a transaction to which you can later roll back. |
| SELECT | S/E | To retrieve data from one or more tables, views, or snapshots, assigning the selected values to host variables. |
| UPDATE | S/E | To change existing values in a table or in a view's base table. |
| VAR | O/D | To override the default datatype and assign a specific Oracle database version 7 external datatype to a host variable. |
| WHENEVER | S/D | To specify handling for error and warning conditions. |
The directives, commands, and clauses appear alphabetically. The description of each contains the following sections:
| Heading | Meaning |
|---|---|
| Purpose | describes the basic uses of the command. |
| Prerequisites | lists privileges you must have and steps that you must take before using the command. Unless otherwise noted, most commands also require that the database be open by your instance. |
| Syntax | shows the keywords and parameters of the command. |
| Keywords and Parameters | describes the purpose of each keyword and parameter. |
| Usage Notes | discusses how and when to use the command. |
| Examples | shows example statements of the command. |
| Related Topics | lists related commands, clauses, and sections of this manual. |
Easy-to-understand syntax diagrams are used to illustrate embedded SQL syntax. They are line-and-arrow drawings that depict valid syntax. If you have never used them, do not worry. This section tells you all you need to know.
Once you understand the logical flow of a syntax diagram, it becomes a helpful guide. You can verify or construct any embedded SQL statement by tracing through its syntax diagram.
Syntax diagrams use lines and arrows to show how commands, parameters, and other language elements are sequenced to form statements. Trace each diagram from left to right, in the direction shown by the arrows. The following symbols will guide you:
Commands and other keywords appear in uppercase. Parameters appear in lowercase. Operators, delimiters, and terminators appear as usual. Following the conventions defined in the Preface, a semicolon terminates statements.
If the syntax diagram has more than one path, you can choose any path to travel.
If you have the choice of more than one keyword, operator, or parameter, your options appear in a vertical list. In the following example, you can travel down the vertical line as far as you like, then continue along any horizontal line:
According to the diagram, all of the following statements are valid:
EXEC SQL WHENEVER NOT FOUND ... EXEC SQL WHENEVER SQLERROR ... EXEC SQL WHENEVER SQLWARNING ...
Required keywords and parameters can appear singly or in a vertical list of alternatives. Single required keywords and parameters appear on the main path, that is, on the horizontal line you are currently traveling. In the following example, cursor is a required parameter:
If there is a cursor named emp_cursor, then, according to the diagram, the following statement is valid:
EXEC SQL CLOSE emp_cursor;
If any of the keywords or parameters in a vertical list appears on the main path, one of them is required. That is, you must choose one of the keywords or parameters, but not necessarily the one that appears on the main path. In the following example, you must choose one of the four actions:
If keywords and parameters appear in a vertical list the main path, they are optional. That is, you need not choose one of them. In the following example, instead of traveling down a vertical line, you can continue along the main path:
If there is a database named oracle2, then, according to the diagram, all of the following statements are valid:
EXEC SQL ROLLBACK; EXEC SQL ROLLBACK WORK; EXEC SQL AT oracle2 ROLLBACK;
Loops let you repeat the syntax within them as many times as you like. In the following example, column_name is inside a loop. So, after choosing one column name, you can go back repeatedly to choose another.
If DEBIT, CREDIT, and BALANCE are column names, then, according to the diagram, all of the following statements are valid:
EXEC SQL SELECT DEBIT INTO ... EXEC SQL SELECT CREDIT, BALANCE INTO ... EXEC SQL SELECT DEBIT, CREDIT, BALANCE INTO ...
Read a multi-part diagram as if all the main paths were joined end-to-end. The following example is a two-part diagram:
According to the diagram, the following statement is valid:
EXEC SQL PREPARE sql_statement FROM :sql_string;
The names of Oracle objects, such as tables and columns, must not exceed 30 characters in length. The first character must be a letter, but the rest can be any combination of letters, numerals, dollar signs ($), pound signs (#), and underscores (_).
However, if an Oracle identifier is enclosed by quotation marks ("), it can contain any combination of legal characters, including spaces but excluding quotation marks.
Oracle identifiers are not case-sensitive except when enclosed by quotation marks.
A cursor variable of type SQL_CURSOR must be declared before allocating memory for the cursor variable.
Whereas a cursor is static, a cursor variable is dynamic because it is not tied to a specific query. You can open a cursor variable for any type-compatible query.
Example
This partial example illustrates the use of the ALLOCATE command in a Pro*C/C++ embedded SQL program:
EXEC SQL BEGIN DECLARE SECTION;
SQL_CURSOR emp_cv;
struct{ ... } emp_rec;
EXEC SQL END DECLARE SECTION;
EXEC SQL ALLOCATE emp_cv;
EXEC SQL EXECUTE
BEGIN
OPEN :emp_cv FOR SELECT * FROM emp;
END;
END-EXEC;
for (;;)
{ EXEC SQL FETCH :emp_cv INTO :emp_rec;
}
"CLOSE (Executable Embedded SQL)", "EXECUTE (Executable Embedded SQL)", and "FETCH (Executable Embedded SQL)"
To disable a cursor, freeing the resources acquired by opening the cursor, and releasing parse locks.
cursor
A cursor to be closed.
cursor_variable
A cursor variable to be closed.
Rows cannot be fetched from a closed cursor. A cursor need not be closed to be reopened. The HOLD_CURSOR and RELEASE_CURSOR precompiler options alter the effect of the CLOSE command. For information on these options, see Chapter 6, "Running the Oracle Precompilers".
"DECLARE CURSOR (Embedded SQL Directive)", "OPEN (Executable Embedded SQL)", and "PREPARE (Executable Embedded SQL)"
To end your current transaction, making permanent all its changes to the database and optionally freeing all resources and disconnecting from the Oracle database version 7 Server.
To commit your current transaction, no privileges are necessary.
To manually commit a distributed in-doubt transaction that you originally committed, you must have FORCE TRANSACTION system privilege. To manually commit a distributed in-doubt transaction that was originally committed by another user, you must have FORCE ANY TRANSACTION system privilege.
If you are using Trusted Oracle database version 7 in DBMS MAC mode, you can only commit an in-doubt transaction if your DBMS label matches the label the transaction's label and the creation label of the user who originally committed the transaction or if you satisfy one of the following criteria:
If the transaction's label or the user's creation label is higher than your DBMS label, you must have READUP and WRITEUP system privileges.
If the transaction's label or the user's creation label is lower than your DBMS label, you must have WRITEDOWN system privilege.
If the transaction's label or the user's creation label is not comparable with your DBMS label, you must have READUP, WRITEUP, and WRITEDOWN system privileges.
AT
Identifies the database to which the COMMIT statement is issued. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, Oracle database version 7 issues the statement to your default database.
Is supported only for compliance with standard SQL. The statements COMMIT and COMMIT WORK are equivalent.
Specifies a comment to be associated with the current transaction. The 'text' is a quoted literal of up to 50 characters that Oracle database version 7 stores in the data dictionary view DBA_2PC_PENDING along with the transaction ID if the transaction becomes in-doubt.
RELEASE
Frees all resources and disconnects the application from the Oracle database version 7 Server.
FORCE
Manually commits an in-doubt distributed transaction. The transaction is identified by the 'text' containing its local or global transaction ID. To find the IDs of such transactions, query the data dictionary view DBA_2PC_PENDING. You can also use the optional integer to explicitly assign the transaction a system change number (SCN). If you omit the integer, the transaction is committed using the current SCN.
Always explicitly commit or rollback the last transaction in your program by using the COMMIT or ROLLBACK command and the RELEASE option. Oracle database version 7 automatically rolls back changes if the program terminates abnormally.
The COMMIT command has no effect on host variables or on the flow of control in the program. For more information on this command, see Chapter 7, "Defining and Controlling Transactions".
This example illustrates the use of the embedded SQL COMMIT command:
EXEC SQL AT sales_db COMMIT RELEASE;
You must have CREATE SESSION system privilege in the specified database.
If you are using Trusted Oracle database version 7 in DBMS MAC mode, your operating system label must dominate both your creation label and the label at which you were granted CREATE SESSION system privilege. Your operating system label must also fall between the operating system equivalents of DBHIGH and DBLOW, inclusive.
If you are using Trusted Oracle database version 7 in operating system MAC mode, your operating system label must match the label of the database to which you are connecting.
:user :password
specifies your username and password separately.
:user_password
is a single host variable containing the Oracle database version 7 username and password separated by a slash (/).
To allow Oracle database version 7 to verify your connection through your operating system, specify "/" as the :user_password value.
AT
identifies the database to which the connection is made. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
USING
specifies the SQL*Net database specification string used to connect to a nondefault database. If you omit this clause, you are connected to your default database.
A program can have multiple connections, but can only connect once to your default database. For more information on this command, see Chapter 3, "Meeting Program Requirements".
Example
The following example illustrate the use of CONNECT:
EXEC SQL CONNECT :username IDENTIFIED BY :password
You can also use this statement in which the value of :userid is the value of :username and :password separated by a "/" such as 'SCOTT/TIGER':
EXEC SQL CONNECT :userid
To declare a cursor, giving it a name and associating it with a SQL statement or a PL/SQL block.
If you associate the cursor with an identifier for a SQL statement or PL/SQL block, you must have declared this identifier in a previous DECLARE STATEMENT statement.
AT
identifies the database on which the cursor is declared. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, Oracle database version 7 declares the cursor on your default database.
cursor
is the name of the cursor to be declared.
SELECT command
is a SELECT statement to be associated with the cursor. The following statement cannot contain an INTO clause.
statement_name block_name
identifies a SQL statement or PL/SQL block to be associated with the cursor. The statement_name or block_name must be previously declared in a DECLARE STATEMENT statement.
You must declare a cursor before referencing it in other embedded SQL statements. The scope of a cursor declaration is global within its precompilation unit and the name of each cursor must be unique in its scope. You cannot declare two cursors with the same name in a single precompilation unit.
You can reference the cursor in the WHERE clause of an UPDATE or DELETE statement using the CURRENT OF syntax, then the cursor has been opened with an OPEN statement and positioned on a row with a FETCH statement. For more information on this command, see Chapter 3, "Meeting Program Requirements".
This example illustrates the use of a DECLARE CURSOR statement:
EXEC SQL DECLARE emp_cursor CURSOR FOR SELECT ename, empno, job, sal FROM emp WHERE deptno = :deptno FOR UPDATE OF sal
"CLOSE (Executable Embedded SQL)", "DECLARE DATABASE (Oracle Embedded SQL Directive)", "DECLARE STATEMENT (Embedded SQL Directive)", "DELETE (Executable Embedded SQL)", "FETCH (Executable Embedded SQL)", "OPEN (Executable Embedded SQL)", "PREPARE (Executable Embedded SQL)", "SELECT (Executable Embedded SQL)", and "UPDATE (Executable Embedded SQL)"
To declare an identifier for a nondefault database to be accessed in subsequent embedded SQL statements.
You declare a db_name for a nondefault database so that other embedded SQL statements can refer to that database using the AT clause. Before issuing a CONNECT statement with an AT clause, you must declare a db_name for the nondefault database with a DECLARE DATABASE statement.
For more information on this command, see Chapter 3, "Meeting Program Requirements".
This example illustrates the use of a DECLARE DATABASE directive:
EXEC SQL DECLARE oracle3 DATABASE
"COMMIT (Executable Embedded SQL)", "CONNECT (Executable Embedded SQL Extension)", "DECLARE CURSOR (Embedded SQL Directive)", "DECLARE STATEMENT (Embedded SQL Directive)", "DELETE (Executable Embedded SQL)", "EXECUTE (Executable Embedded SQL)", "EXECUTE IMMEDIATE (Executable Embedded SQL)", "INSERT (Executable Embedded SQL)", "SELECT (Executable Embedded SQL)", and "UPDATE (Executable Embedded SQL)"
To declare an identifier for a SQL statement or PL/SQL block to be used in other embedded SQL statements.
AT
identifies the database on which the SQL statement or PL/SQL block is declared. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, Oracle database version 7 declares the SQL statement or PL/SQL block on your default database.
statement_name block_name
is the declared identifier for the statement.
You must declare an identifier for a SQL statement or PL/SQL block with a DECLARE STATEMENT statement only if a DECLARE CURSOR statement referencing the identifier appears physically (not logically) in the embedded SQL program before the PREPARE statement that parses the statement or block and associates it with its identifier.
The scope of a statement declaration is global within its precompilation unit, like a cursor declaration.For more information on this command, see Chapter 3, "Meeting Program Requirements" and Chapter 10, "Using Dynamic SQL".
This example illustrates the use of the DECLARE STATEMENT statement:
EXEC SQL AT remote_db DECLARE my_statement STATEMENT EXEC SQL PREPARE my_statement FROM :my_string EXEC SQL EXECUTE my_statement
In this example from a Pro*C/C++ embedded SQL program, the DECLARE STATEMENT statement is required because the DECLARE CURSOR statement precedes the PREPARE statement:
EXEC SQL DECLARE my_statement STATEMENT; EXEC SQL DECLARE emp_cursor CURSOR FOR my_statement; EXEC SQL PREPARE my_statement FROM :my_string; ...
To define the structure of a table or view, including each column's datatype, default value, and NULL or NOT NULL specification for semantic checking by the Oracle Precompilers.
table
is the name of the declared table.
column
is a column of the table.
datatype
is the datatype of a column.
DEFAULT
specifies the default value of a column.
NULL
specifies that a column can contain nulls.
NOT NULL
specifies that a column cannot contain nulls.
WITH DEFAULT
is supported for compatibility with the IBM DB2 database.
For information on using this command, see Chapter 3, "Meeting Program Requirements".
For you to delete rows from a table, the table must be in your own schema or you must have DELETE privilege on the table.
For you to delete rows from the base table of a view, the owner of the schema containing the view must have DELETE privilege on the base table. Also, if the view is in a schema other than your own, you must be granted DELETE privilege on the view.
The DELETE ANY TABLE system privilege also enables delete rows from any table or any view's base table.
If you are using Trusted Oracle database version 7 in DBMS MAC mode, your DBMS label must dominate the creation label of the table or view or you must meet one of the following criteria:
If the creation label of the table or view is higher than your DBMS label, you must have READUP and WRITEUP system privileges.
If the creation label of your table or view is not comparable to your DBMS label, you must have READUP, WRITEUP, and WRITEDOWN system privileges.
In addition, for each row to be deleted, your DBMS label must match the row's label or you must meet one of the following criteria:
If the row's label is higher than your DBMS label, you must have READUP and WRITEUP system privileges.
If the row's label is lower than your DBMS label, you must have WRITEDOWN system privilege.
If the row label is not comparable to your DBMS label, you must have READUP, WRITEUP, and WRITEDOWN system privileges.
AT
identifies the database to which the DELETE statement is issued. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, the DELETE statement is issued to your default database.
FOR :host_integer
limits the number of times the statement is executed if the WHERE clause contains array host variables. If you omit this clause, Oracle database version 7 executes the statement once for each component of the smallest array.
schema
is the schema containing the table or view. If you omit schema, Oracle database version 7 assumes the table or view is in your own schema.
table view
is the name of a table from which the rows are to be deleted. If you specify view, Oracle database version 7 deletes rows from the view's base table.
dblink
is the complete or partial name of a database link to a remote database where the table or view is located. You can only delete rows from a remote table or view if you are using Oracle database version 7 with the distributed option.
If you omit dblink, Oracle database version 7 assumes that the table or view is located on the local database.
alias
is an alias assigned to the table. Aliases are generally used in DELETE statements with correlated queries.
specifies which rows are deleted:
condition deletes only rows that satisfy the condition. This condition can contain host variables and optional indicator variables.
CURRENT OF deletes only the row most recently fetched by the cursor. The cursor cannot be associated with a SELECT statement that performs a join, unless its FOR UPDATE clause specifically locks only one table.
If you omit this clause entirely, Oracle database version 7 deletes all rows from the table or view.
The host variables in the WHERE clause must be either all scalars or all arrays. If they are scalars, Oracle database version 7 executes the DELETE statement only once. If they are arrays, Oracle database version 7 executes the statement once for each set of array components. Each execution may delete zero, one, or multiple rows.
Array host variables in the WHERE clause can have different sizes. In this case, the number of times Oracle database version 7 executes the statement is determined by the smaller of the following values:
the size of the smallest array
the value of the :host_integer in the optional FOR clause
If no rows satisfy the condition, no rows are deleted and the SQLCODE returns a NOT_FOUND condition.
The cumulative number of rows deleted is returned through the SQLCA. If the WHERE clause contains array host variables, this value reflects the total number of rows deleted for all components of the array processed by the DELETE statement.
If no rows satisfy the condition, Oracle database version 7 returns an error through the SQLCODE of the SQLCA. If you omit the WHERE clause, Oracle database version 7 raises a warning flag in the fifth component of SQLWARN in the SQLCA. For more information on this command and the SQLCA, see Chapter 8, "Error Handling and Diagnostics".
You can use comments in a DELETE statement to pass instructions, or hints, to the Oracle database version 7 optimizer. The optimizer uses hints to choose an execution plan for the statement.
This example illustrates the use of the DELETE statement within a Pro*C/C++ embedded SQL program:
EXEC SQL DELETE FROM emp WHERE deptno = :deptno AND job = :job; ... EXEC SQL DECLARE emp_cursor CURSOR FOR SELECT empno, comm FROM emp; EXEC SQL OPEN emp_cursor; EXEC SQL FETCH c1 INTO :emp_number, :commission; EXEC SQL DELETE FROM emp WHERE CURRENT OF emp_cursor;
"DECLARE DATABASE (Oracle Embedded SQL Directive)" and "DECLARE STATEMENT (Embedded SQL Directive)"
To initialize a descriptor to hold descriptions of host variables for a dynamic SQL statement or PL/SQL block.
You must have prepared the SQL statement or PL/SQL block in a previous embedded SQL PREPARE statement.
BIND VARIABLES
initializes the descriptor to hold information about the input variables for the SQL statement or PL/SQL block.
SELECT LIST
initializes the descriptor to hold information about the select list of a SELECT statement.
The default is SELECT LIST FOR.
statement_name block_name
identifies a SQL statement or PL/SQL block previously prepared with a PREPARE statement.
descriptor
is the name of the descriptor to be initialized.
You must issue a DESCRIBE statement before manipulating the bind or select descriptor within an embedded SQL program.
You cannot describe both input variables and output variables into the same descriptor.
The number of variables found by a DESCRIBE statement is the total number of placeholders in the prepare SQL statement or PL/SQL block, rather than the total number of uniquely named placeholders. For more information on this command, see Chapter 10, "Using Dynamic SQL".
This example illustrates the use of the DESCRIBE statement in a Pro*C embedded SQL program:
EXEC SQL PREPARE my_statement FROM :my_string; EXEC SQL DECLARE emp_cursor FOR SELECT empno, ename, sal, comm FROM emp WHERE deptno = :dept_number EXEC SQL DESCRIBE BIND VARIABLES FOR my_statement INTO bind_descriptor; EXEC SQL OPEN emp_cursor USING bind_descriptor; EXEC SQL DESCRIBE SELECT LIST FOR my_statement INTO select_descriptor; EXEC SQL FETCH emp_cursor INTO select_descriptor;
AT
identifies the database on which the PL/SQL block is executed. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, the PL/SQL block is executed on your default database.
pl/sql_block
END-EXEC
must appear after the embedded PL/SQL block, regardless of which programming language your Oracle Precompiler program uses. Of course, the keyword END-EXEC must be followed by the embedded SQL statement terminator for the specific language.
Since the Oracle Precompilers treat an embedded PL/SQL block like a single embedded SQL statement, you can embed a PL/SQL block anywhere in an Oracle Precompiler program that you can embed a SQL statement. For more information on embedding PL/SQL blocks in Oracle Precompiler programs, see Chapter 5, "Using Embedded PL/SQL"
Placing this EXECUTE statement in an Oracle Precompiler program embeds a PL/SQL block in the program:
EXEC SQL EXECUTE BEGIN SELECT ename, job, sal INTO :emp_name:ind_name, :job_title, :salary FROM emp WHERE empno = :emp_number; IF :emp_name:ind_name IS NULL THEN RAISE name_missing; END IF; END; END-EXEC
To execute a DELETE, INSERT, or UPDATE statement or a PL/SQL block that has been previously prepared with an embedded SQL PREPARE statement.
You must first prepare the SQL statement or PL/SQL block with an embedded SQL PREPARE statement.
limits the number of times the statement is executed when the USING clause contains array host variables If you omit this clause, Oracle database version 7 executes the statement once for each component of the smallest array.
statement_id
is a precompiler identifier associated with the SQL statement or PL/SQL block to be executed. Use the embedded SQL PREPARE command to associate the precompiler identifier with the statement or PL/SQL block.
specifies a list of host variables with optional indicator variables that Oracle database version 7 substitutes as input variables into the statement to be executed. The host and indicator variables must be either all scalars or all arrays.
This example illustrates the use of the EXECUTE statement in a Pro*C/C++ embedded SQL program:
EXEC SQL PREPARE my_statement FROM :my_string; EXEC SQL EXECUTE my_statement USING :my_var;
"DECLARE DATABASE (Oracle Embedded SQL Directive)" and "PREPARE (Executable Embedded SQL)"
To prepare and execute a DELETE, INSERT, or UPDATE statement or a PL/SQL block containing no host variables.
AT
identifies the database on which the SQL statement or PL/SQL block is executed. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, the statement or block is executed on your default database.
:host_string
is a host variable whose value is the SQL statement or PL/SQL block to be executed.
text
is a quoted text literal containing the SQL statement or PL/SQL block to be executed.
The SQL statement can only be a DELETE, INSERT, or UPDATE statement.
When you issue an EXECUTE IMMEDIATE statement, Oracle database version 7 parses the specified SQL statement or PL/SQL block, checking for errors, and executes it. If any errors are encountered, they are returned in the SQLCODE component of the SQLCA.
For more information on this command, see Chapter 10, "Using Dynamic SQL".
To retrieve one or more rows returned by a query, assigning the select list values to host variables.
FOR :host_integer
limits the number of rows fetched if you are using array host variables. If you omit this clause, Oracle database version 7 fetches enough rows to fill the smallest array.
cursor
is a cursor that is declared by a DECLARE CURSOR statement. The FETCH statement returns one of the rows selected by the query associated with the cursor.
:cursor_variable
is a cursor variable is allocated an ALLOCATE statement. The FETCH statement returns one of the rows selected by the query associated with the cursor variable.
specifies a list of host variables and optional indicator variables into which data is fetched. These host variables and indicator variables must be declared within the program.
specifies the descriptor referenced in a previous DESCRIBE statement. Only use this clause with dynamic embedded SQL, method 4. Also, the USING clause does not apply when a cursor variable is used.
The FETCH statement reads the rows of the active set and names the output variables which contain the results. Indicator values are set to -1 if their associated host variable is null. The first FETCH statement for a cursor also sorts the rows of the active set, if necessary.
The number of rows retrieved is specified by the size of the output host variables and the value specified in the FOR clause. The host variables to receive the data must be either all scalars or all arrays. If they are scalars, Oracle database version 7 fetches only one row. If they are arrays, Oracle database version 7 fetches enough rows to fill the arrays.
Array host variables can have different sizes. In this case, the number of rows Oracle database version 7 fetches is determined by the smaller of the following values:
The size of the smallest array
The value of the :host_integer in the optional FOR clause
Of course, the number of rows fetched can be further limited by the number of rows that actually satisfy the query.
If a FETCH statement does not retrieve all rows returned by the query, the cursor is positioned on the next returned row. When the last row returned by the query has been retrieved, the next FETCH statement results in an error code returned in the SQLCODE element of the SQLCA.
Note that the FETCH command does not contain an AT clause. You must specify the database accessed by the cursor in the DECLARE CURSOR statement.
You can only move forward through the active set with FETCH statements. If you want to revisit any of the previously fetched rows, you must reopen the cursor and fetch each row in turn. If you want to change the active set, you must assign new values to the input host variables in the cursor's query and reopen the cursor.
This example illustrates the FETCH command in a pseudo-code embedded SQL program:
EXEC SQL DECLARE emp_cursor CURSOR FOR SELECT job, sal FROM emp WHERE deptno = 30; ... EXEC SQL WHENEVER NOT FOUND GOTO ... LOOP EXEC SQL FETCH emp_cursor INTO :job_title1, :salary1; EXEC SQL FETCH emp_cursor INTO :job_title2, :salary2; ... END LOOP; ...
For you to insert rows into a table, the table must be in your own schema or you must have INSERT privilege on the table.
For you to insert rows into the base table of a view, the owner of the schema containing the view must have INSERT privilege on the base table. Also, if the view is in a schema other than your own, you must have INSERT privilege on the view.
The INSERT ANY TABLE system privilege also enables insert rows into any table or any view's base table.
If you are using Trusted Oracle database version 7 in DBMS MAC mode, your DBMS label must match the creation label of the table or view:
If the creation label of the table or view is higher than your DBMS label, you must have WRITEUP system privileges.
If the creation label of the table or view is lower than your DBMS label, you must have WRITEDOWN system privilege.
If the creation label of your table or view is not comparable to your DBMS label, you must have WRITEUP and WRITEDOWN system privileges.
AT
identifies the database on which the INSERT statement is executed. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name
If you omit this clause, the INSERT statement is executed on your default database.
limits the number of times the statement is executed if the VALUES clause contains array host variables. If you omit this clause, Oracle database version 7 executes the statement once for each component in the smallest array.
schema
is the schema containing the table or view. If you omit schema, Oracle database version 7 assumes the table or view is in your own schema.
table view
is the name of the table into which rows are to be inserted. If you specify view, Oracle database version 7 inserts rows into the view's base table.
dblink
is a complete or partial name of a database link to a remote database where the table or view is located. You can only insert rows into a remote table or view if you are using Oracle database version 7 with the distributed option.
If you omit dblink, Oracle database version 7 assumes that the table or view is on the local database.
column
is a column of the table or view. In the inserted row, each column in this list is assigned a value from the VALUES clause or the query.
If you omit one of the table's columns from this list, the column's value for the inserted row is the column's default value as specified when the table was created. If you omit the column list altogether, the VALUES clause or query must specify values for all columns in the table.
specifies a row of values to be inserted into the table or view. Note that the expressions can be host variables with optional indicator variables. You must specify an expression in the VALUES clause for each column in the column list.
subquery
is a subquery that returns rows that are inserted into the table. The select list of this subquery must have the same number of columns as the column list of the INSERT statement.
Any host variables that appear in the WHERE clause must be either all scalars or all arrays. If they are scalars, Oracle database version 7 executes the INSERT statement once. If they are arrays, Oracle database version 7 executes the INSERT statement once for each set of array components, inserting one row each time.
Array host variables in the WHERE clause can have different sizes. In this case, the number of times Oracle database version 7 executes the statement is determined by the smaller of the following values:
size of the smallest array
the value of the :host_integer in the optional FOR clause.
For more information on this command, see Chapter 4, " Using Embedded SQL".
This example illustrates the use of the embedded SQL INSERT command:
EXEC SQL INSERT INTO emp (ename, empno, sal) VALUES (:ename, :empno, :sal);
To open a cursor, evaluating the associated query and substituting the host variable names supplied by the USING clause into the WHERE clause of the query.
You must declare the cursor with a DECLARE CURSOR embedded SQL statement before opening it.
cursor
is the cursor to be opened.
specifies the host variables to be substituted into the WHERE clause of the associated query.
:host_variable specifies a host variable with an optional indicator variable to be substituted into the statement associated with the cursor.
DESCRIPTOR
specifies a descriptor that describes the host variables to be substituted into the WHERE clause of the associated query. The descriptor must be initialized in a previous DESCRIBE statement.
The substitution is based on position. The host variable names specified in this statement can be different from the variable names in the associated query.
The OPEN command defines the active set of rows and initializes the cursor just before the first row of the active set. The values of the host variables at the time of the OPEN are substituted in the statement. This command does not actually retrieve rows; rows are retrieved by the FETCH command.
Once you have opened a cursor, its input host variables are not reexamined until you reopen the cursor. To change any input host variables and therefore the active set, you must reopen the cursor.
All cursors in a program are in a closed state when the program is initiated or when they have been explicitly closed using the CLOSE command.
You can reopen a cursor without first closing it. For more information on this command, see Chapter 4, " Using Embedded SQL".
To parse a SQL statement or PL/SQL block specified by a host variable and associate it with an identifier.
statement_id
is the identifier to be associated with the prepared SQL statement or PL/SQL block. If this identifier was previously assigned to another statement or block, the prior assignment is superseded.
:host_string
is a host variable whose value is the text of a SQL statement or PL/SQL block to be prepared.
text
is a string literal containing a SQL statement or PL/SQL block to be prepared.
Any variables that appear in the :host_string or text are placeholders. The actual host variable names are assigned in the USING clause of the OPEN command (input host variables) or in the INTO clause of the FETCH command (output host variables).
A SQL statement is prepared only once, but can be executed any number of times.
To undo work done in the current transaction.
You can also use this command to manually undo the work done by an in-doubt distributed transaction.
To roll back your current transaction, no privileges are necessary.
To manually roll back an in-doubt distributed transaction that you originally committed, you must have FORCE TRANSACTION system privilege. To manually roll back an in-doubt distributed transaction originally committed by another user, you must have FORCE ANY TRANSACTION system privilege.
is optional and is provided for ANSI compatibility.
rolls back the current transaction to the specified savepoint. If you omit this clause, the ROLLBACK statement rolls back the entire transaction.
FORCE
manually rolls back an in-doubt distributed transaction. The transaction is identified by thetext containing its local or global transaction ID. To find the IDs of such transactions, query the data dictionary view DBA_2PC_PENDING.
ROLLBACK statements with the FORCE clause are not supported in PL/SQL.
RELEASE
frees all resources and disconnects the application from the Oracle database version 7 Server. The RELEASE clause is not allowed with SAVEPOINT and FORCE clauses.
A transaction (or a logical unit of work) is a sequence of SQL statements that Oracle database version 7 treats as a single unit. A transaction begins with the first executable SQL statement after a COMMIT, ROLLBACK or connection to the database. A transaction ends with a COMMIT statement, a ROLLBACK statement, or disconnection (intentional or unintentional) from the database. Note that Oracle database version 7 issues an implicit COMMIT statement before and after processing any data definition language statement.
Using the ROLLBACK command without the TO SAVEPOINT clause performs the following operations:
ends the transaction
undoes all changes in the current transaction
erases all savepoints in the transaction
releases the transaction's locks
Using the ROLLBACK command with the TO SAVEPOINT clause performs the following operations:
rolls back just the portion of the transaction after the savepoint.
loses all savepoints created after that savepoint. Note that the named savepoint is retained, so you can roll back to the same savepoint multiple times. Prior savepoints are also retained.
releases all table and row locks acquired since the savepoint. Note that other transactions that have requested access to rows locked after the savepoint must continue to wait until the transaction is committed or rolled back. Other transactions that have not already requested the rows can request and access the rows immediately.
It is recommended that you explicitly end transactions in application programs using either a COMMIT or ROLLBACK statement. If you do not explicitly commit the transaction and the program terminates abnormally, Oracle database version 7 rolls back the last uncommitted transaction.
The following statement rolls back your entire current transaction:
EXEC SQL ROLLBACK;
The following statement rolls back your current transaction to savepoint SP5:
EXEC SQL ROLLBACK TO SAVEPOINT sp5;
Oracle database version 7 with the distributed option enables perform distributed transactions, or transactions that modify data on multiple databases. To commit or roll back a distributed transaction, you need only issue a COMMIT or ROLLBACK statement as you would any other transaction.
If there is a network failure during the commit process for a distributed transaction, the state of the transaction may be unknown, or in-doubt. After consultation with the administrators of the other databases involved in the transaction, you may decide to manually commit or roll back the transaction on your local database. You can manually roll back the transaction on your local database by issuing a ROLLBACK statement with the FORCE clause.
You cannot manually roll back an in-doubt transaction to a savepoint.
A ROLLBACK statement with a FORCE clause only rolls back the specified transaction. Such a statement does not affect your current transaction.
AT
identifies the database on which the savepoint is created. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, the savepoint is created on your default database.
savepoint
is the name of the savepoint to be created.
For more information on this command, see Chapter 7, "Defining and Controlling Transactions".
Example
This example illustrates the use of the embedded SQL SAVEPOINT command:
EXEC SQL SAVEPOINT save3;
To retrieve data from one or more tables, views, or snapshots, assigning the selected values to host variables.
For you to select data from a table or snapshot, the table or snapshot must be in your own schema or you must have SELECT privilege on the table or snapshot.
For you to select rows from the base tables of a view, the owner of the schema containing the view must have SELECT privilege on the base tables. Also, if the view is in a schema other than your own, you must have SELECT privilege on the view.
The SELECT ANY TABLE system privilege also enables select data from any table or any snapshot or any view's base table.
If you are using Trusted Oracle database version 7 in DBMS MAC mode, your DBMS label must dominate the creation label of each queried table, view, or snapshot or you must have READUP system privileges.
AT
identifies the database to which the SELECT statement is issued. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, the SELECT statement is issued to your default database.
select_list
identical to the non-embedded SELECT command except that a host variables can be used in place of literals.
specifies output host variables and optional indicator variables to receive the data returned by the SELECT statement. Note that these variables must be either all scalars or all arrays, but arrays need not have the same size.
WHERE
restricts the rows returned to those for which the condition is TRUE. The condition can contain host variables, but cannot contain indicator variables. These host variables can be either scalars or arrays.
All other keywords and parameters are identical to the non-embedded SQL SELECT command.
If no rows meet the WHERE clause condition, no rows are retrieved and Oracle database version 7 returns an error code through the SQLCODE component of the SQLCA.
You can use comments in a SELECT statement to pass instructions, or hints, to the Oracle database version 7 optimizer. The optimizer uses hints to choose an execution plan for the statement. For more information on hints, see Oracle database version 7 Server Tuning.
For you to update values in a table or snapshot, the table must be in your own schema or you must have UPDATE privilege on the table.
For you to update values in the base table of a view, the owner of the schema containing the view must have UPDATE privilege on the base table. Also, if the view is in a schema other than your own, you must have UPDATE privilege on the view.
The UPDATE ANY TABLE system privilege also enables update values in any table or any view's base table.
If you are using Trusted Oracle database version 7 in DBMS MAC mode, your DBMS label must match the creation label of the table or view:
If the creation label of the table or view is higher than your DBMS label, you must have READUP and WRITEUP system privileges
If the creation label of the table or view is lower than your DBMS label, you must have WRITEDOWN system privilege.
If the creation label of your table or view is not comparable to your DBMS label, you must have READUP, WRITEUP, and WRITEDOWN system privileges.
AT
identifies the database to which the UPDATE statement is issued. The database can be identified by either:
db_name is a database identifier declared in a previous DECLARE DATABASE statement.
:host_variable is a host variable whose value is a previously declared db_name.
If you omit this clause, the UPDATE statement is issued to your default database.
FOR :host_integer
limits the number of times the UPDATE statement is executed if the SET and WHERE clauses contain array host variables. If you omit this clause, Oracle database version 7 executes the statement once for each component of the smallest array.
schema
is the schema containing the table or view. If you omit schema, Oracle database version 7 assumes the table or view is in your own schema.
table view
is the name of the table to be updated. If you specify view, Oracle database version 7 updates the view's base table.
dblink
is a complete or partial name of a database link to a remote database where the table or view is located. You can only use a database link to update a remote table or view if you are using Oracle database version 7 with the distributed option.
alias
is a name used to reference the table, view, or subquery elsewhere in the statement.
column
is the name of a column of the table or view that is to be updated. If you omit a column of the table from the SET clause, that column's value remains unchanged.
expr
is the new value assigned to the corresponding column. This expression can contain host variables and optional indicator variables.
subquery_1
is a subquery that returns new values that are assigned to the corresponding columns.
subquery_2
is a subquery that return a new value that is assigned to the corresponding column.
specifies which rows of the table or view are updated:
condition updates only rows for which this condition is true. This condition can contain host variables and optional indicator variables.
CURRENT OF updates only the row most recently fetched by thecursor. The cursor cannot be associated with a SELECT statement that performs a join unless its FOR UPDATE clause explicitly locks only one table.
If you omit this clause entirely, Oracle database version 7 updates all rows of the table or view.
Host variables in the SET and WHERE clauses must be either all scalars or all arrays. If they are scalars, Oracle database version 7 executes the UPDATE statement only once. If they are arrays, Oracle database version 7 executes the statement once for each set of array components. Each execution may update zero, one, or multiple rows.
Array host variables can have different sizes. In this case, the number of times Oracle database version 7 executes the statement is determined by the smaller of the following values:
the size of the smallest array
the value of the :host_integer in the optional FOR clause
The cumulative number of rows updated is returned through the third element of the SQLERRD component of the SQLCA. When arrays are used as input host variables, this count reflects the total number of updates for all components of the array processed in the UPDATE statement. If no rows satisfy the condition, no rows are updated and Oracle database version 7 returns an error message through the SQLCODE element of the SQLCA. If you omit the WHERE clause, all rows are updated and Oracle database version 7 raises a warning flag in the fifth component of the SQLWARN element of the SQLCA.
You can use comments in an UPDATE statement to pass instructions, or hints, to the Oracle database version 7 optimizer. The optimizer uses hints to choose an execution plan for the statement.
For more information on this command, see Chapter 4, " Using Embedded SQL" and Chapter 7, "Defining and Controlling Transactions".
To perform host variable equivalencing, or to assign a specific Oracle database version 7 external datatype to an individual host variable, overriding the default datatype assignment.
The host variable must be previously declared in the Declare Section of the embedded SQL program.
host_variable
is the host variable to be assigned an Oracle database version 7 external datatype.
datatype
is an Oracle database version 7 external datatype recognized by the Oracle Precompilers (not an Oracle database version 7 internal datatype). The datatype may include a length, precision, or scale. This external datatype is assigned to the host_variable. For a list of external datatypes, see Chapter 3, "Meeting Program Requirements".
Host variable equivalencing is one kind of datatype equivalencing. Datatype equivalencing is useful for any of the following purposes:
to automatically null-terminate a character host variable
to store program data as binary data in the database
to override default datatype conversion
This example equivalences the host variable DEPT_NAME to
the datatype STRING and the host variable BUFFER to the datatype RAW(2000):
EXEC SQL BEGIN DECLARE SECTION; ... dept_name CHARACTER(15); -- default datatype is CHAR EXEC SQL VAR dept_name IS STRING; -- reset to STRING ... buffer CHARACTER(200); -- default datatype is CHAR EXEC SQL VAR buffer IS RAW(200); -- refer to RAW ... EXEC SQL END DECLARE SECTION;
To specify the action to be taken when an error or warning results from executing an embedded SQL program.
The following syntax diagram shows how to construct a WHENEVER statement:
identifies any exception condition that returns an error code of +1403 to SQLCODE (or a +100 code when MODE=ANSI).
identifies a condition that results in a negative return code.
identifies a non-fatal warning condition.
CONTINUE
indicates that the program should progress to the next statement.
GOTO
indicates that the program should branch to the statement named bylabel.
stops program execution.
DO
indicates that the program should call a host language routine. The syntax ofroutine depends on your host language. See your language-specific Supplement to the Oracle Precompilers Guide.
The WHENEVER command allows your program to transfer control to an error handling routine in the event an embedded SQL statement results in an error or warning.
The scope of a WHENEVER statement is positional, rather than logical. A WHENEVER statement applies to all embedded SQL statements that textually follow it in the source file, not in the flow of the program logic. A WHENEVER statement remains in effect until it is superseded by another WHENEVER statement checking for the same condition.
For more information on this command, see Chapter 7, "Defining and Controlling Transactions". Do not confuse the WHENEVER embedded SQL command with the WHENEVER SQL*Plus command.
