Literals

Text Literals

Use the text literal notation to specify values whenever 'string' or appears in the syntax of expressions, conditions, SQL functions, and SQL statements in other parts of this reference. This reference uses the terms text literal, character literal, and string interchangeably. Text, character, and string literals are always surrounded by single quotation marks. If the syntax uses the term char, you can specify either a text literal or another expression that resolves to character data — for example, the last_name column of the hr.employees table. When char appears in the syntax, the single quotation marks are not used.

The syntax of text literals is as follows:

text::=

Description of the illustration text.gif

where N or n specifies the literal using the national character set (NCHAR or NVARCHAR2 data). By default, text entered using this notation is translated into the national character set by way of the database character set when used by the server. To avoid potential loss of data during the text literal conversion to the database character set, set the environment variable ORA_NCHAR_LITERAL_REPLACE to TRUE. Doing so transparently replaces the n' internally and preserves the text literal for SQL processing.

In the top branch of the syntax:

• c is any member of the user's character set. A single quotation mark (') within the literal must be preceded by an escape character. To represent one single quotation mark within a literal, enter two single quotation marks.

• ' ' are two single quotation marks that begin and end text literals.

In the bottom branch of the syntax:

• Q or q indicates that the alternative quoting mechanism will be used. This mechanism allows a wide range of delimiters for the text string.

• The outermost ' ' are two single quotation marks that precede and follow, respectively, the opening and closing quote_delimiter.

• c is any member of the user's character set. You can include quotation marks (") in the text literal made up of c characters. You can also include the quote_delimiter, as long as it is not immediately followed by a single quotation mark.

• quote_delimiter is any single- or multibyte character except space, tab, and return. The quote_delimiter can be a single quotation mark. However, if the quote_delimiter appears in the text literal itself, ensure that it is not immediately followed by a single quotation mark.

  If the opening quote_delimiter is one of [, {, <, or (, then the closing quote_delimiter must be the corresponding ], }, >, or ). In all other cases, the opening and closing quote_delimiter must be the same character.

Text literals have properties of both the CHAR and VARCHAR2 datatypes:

• Within expressions and conditions, Oracle treats text literals as though they have the datatype CHAR by comparing them using blank-padded comparison semantics.

• A text literal can have a maximum length of 4000 bytes.

Here are some valid text literals:

'Hello'
'ORACLE.dbs'
'Jackie''s raincoat'
'09-MAR-98'
N'nchar literal'

Here are some valid text literals using the alternative quoting mechanism:

q'!name LIKE '%DBMS_%%'!'
q'<'So,' she said, 'It's finished.'>'
q'{SELECT * FROM employees WHERE last_name = 'Smith';}'
nq'ï Ÿ1234 ï'
q'"name like '['"'

Numeric Literals

Use numeric literal notation to specify fixed and floating-point numbers.

Datetime Literals

Oracle Database supports four datetime datatypes: DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, and TIMESTAMP WITH LOCAL TIME ZONE.

Date Literals You can specify a DATE value as a string literal, or you can convert a character or numeric value to a date value with the TO_DATE function. DATE literals are the only case in which Oracle Database accepts a TO_DATE expression in place of a string literal.

To specify a DATE value as a literal, you must use the Gregorian calendar. You can specify an ANSI literal, as shown in this example:

DATE '1998-12-25'

The ANSI date literal contains no time portion, and must be specified in exactly this format ('YYYY-MM-DD'). Alternatively you can specify an Oracle date value, as in the following example:

TO_DATE('98-DEC-25 17:30','YY-MON-DD HH24:MI')

The default date format for an Oracle DATE value is specified by the initialization parameter NLS_DATE_FORMAT. This example date format includes a two-digit number for the day of the month, an abbreviation of the month name, the last two digits of the year, and a 24-hour time designation.

Oracle automatically converts character values that are in the default date format into date values when they are used in date expressions.

If you specify a date value without a time component, then the default time is midnight (00:00:00 or 12:00:00 for 24-hour and 12-hour clock time, respectively). If you specify a date value without a date, then the default date is the first day of the current month.

Oracle DATE columns always contain both the date and time fields. Therefore, if you query a DATE column, then you must either specify the time field in your query or ensure that the time fields in the DATE column are set to midnight. Otherwise, Oracle may not return the query results you expect. You can use the TRUNC (date) function to set the time field to midnight, or you can include a greater-than or less-than condition in the query instead of an equality or inequality condition.

Here are some examples that assume a table my_table with a number column row_num and a DATE column datecol:

INSERT INTO my_table VALUES (1, SYSDATE);
INSERT INTO my_table VALUES (2, TRUNC(SYSDATE));

SELECT * FROM my_table;

   ROW_NUM DATECOL
---------- ---------
         1 03-OCT-02
         2 03-OCT-02

SELECT * FROM my_table
   WHERE datecol = TO_DATE('03-OCT-02','DD-MON-YY');

   ROW_NUM DATECOL
---------- ---------
         2 03-OCT-02

SELECT * FROM my_table
   WHERE datecol > TO_DATE('02-OCT-02', 'DD-MON-YY');

   ROW_NUM DATECOL
---------- ---------
         1 03-OCT-02
         2 03-OCT-02

If you know that the time fields of your DATE column are set to midnight, then you can query your DATE column as shown in the immediately preceding example, or by using the DATE literal:

SELECT * FROM my_table WHERE datecol = DATE '2002-10-03';

However, if the DATE column contains values other than midnight, then you must filter out the time fields in the query to get the correct result. For example:

SELECT * FROM my_table WHERE TRUNC(datecol) = DATE '2002-10-03';

Oracle applies the TRUNC function to each row in the query, so performance is better if you ensure the midnight value of the time fields in your data. To ensure that the time fields are set to midnight, use one of the following methods during inserts and updates:

• Use the TO_DATE function to mask out the time fields:

  INSERT INTO my_table VALUES 
     (3, TO_DATE('3-OCT-2002','DD-MON-YYYY'));
  
  

• Use the DATE literal:

  INSERT INTO my_table VALUES (4, '03-OCT-02');
  
  

• Use the TRUNC function:

  INSERT INTO my_table VALUES (5, TRUNC(SYSDATE));
  
  

The date function SYSDATE returns the current system date and time. The function CURRENT_DATE returns the current session date. For information on SYSDATE, the TO_* datetime functions, and the default date format, see "Datetime Functions".

TIMESTAMP Literals The TIMESTAMP datatype stores year, month, day, hour, minute, and second, and fractional second values. When you specify TIMESTAMP as a literal, the fractional_seconds_precision value can be any number of digits up to 9, as follows:

TIMESTAMP '1997-01-31 09:26:50.124'

TIMESTAMP WITH TIME ZONE Literals The TIMESTAMP WITH TIME ZONE datatype is a variant of TIMESTAMP that includes a time zone offset. When you specify TIMESTAMP WITH TIME ZONE as a literal, the fractional_seconds_precision value can be any number of digits up to 9. For example:

TIMESTAMP '1997-01-31 09:26:56.66 +02:00'

Two TIMESTAMP WITH TIME ZONE values are considered identical if they represent the same instant in UTC, regardless of the TIME ZONE offsets stored in the data. For example,

TIMESTAMP '1999-04-15 8:00:00 -8:00'

is the same as

TIMESTAMP '1999-04-15 11:00:00 -5:00'

That is, 8:00 a.m. Pacific Standard Time is the same as 11:00 a.m. Eastern Standard Time.

You can replace the UTC offset with the TZR (time zone region) format element. For example, the following example has the same value as the preceding example:

TIMESTAMP '1999-04-15 8:00:00 US/Pacific'

To eliminate the ambiguity of boundary cases when the daylight saving time switches, use both the TZR and a corresponding TZD format element. The following example ensures that the preceding example will return a daylight saving time value:

TIMESTAMP '1999-10-29 01:30:00 US/Pacific PDT'

You can also express the time zone offset using a datetime expression:

SELECT TIMESTAMP '1999-10-29 01:30:00' AT TIME ZONE 'US/Pacific' FROM DUAL;

If you do not add the TZD format element, and the datetime value is ambiguous, then Oracle returns an error if you have the ERROR_ON_OVERLAP_TIME session parameter set to TRUE. If that parameter is set to FALSE, then Oracle interprets the ambiguous datetime as standard time in the specified region.

TIMESTAMP WITH LOCAL TIME ZONE Literals The TIMESTAMP WITH LOCAL TIME ZONE datatype differs from TIMESTAMP WITH TIME ZONE in that data stored in the database is normalized to the database time zone. The time zone offset is not stored as part of the column data. There is no literal for TIMESTAMP WITH LOCAL TIME ZONE. Rather, you represent values of this datatype using any of the other valid datetime literals. The table that follows shows some of the formats you can use to insert a value into a TIMESTAMP WITH LOCAL TIME ZONE column, along with the corresponding value returned by a query.

Notice that if the value specified does not include a time component (either explicitly or implicitly, then the value returned defaults to midnight.

Interval Literals

An interval literal specifies a period of time. You can specify these differences in terms of years and months, or in terms of days, hours, minutes, and seconds. Oracle Database supports two types of interval literals, YEAR TO MONTH and DAY TO SECOND. Each type contains a leading field and may contain a trailing field. The leading field defines the basic unit of date or time being measured. The trailing field defines the smallest increment of the basic unit being considered. For example, a YEAR TO MONTH interval considers an interval of years to the nearest month. A DAY TO MINUTE interval considers an interval of days to the nearest minute.

If you have date data in numeric form, then you can use the NUMTOYMINTERVAL or NUMTODSINTERVAL conversion function to convert the numeric data into interval values.

Interval literals are used primarily with analytic functions.