20
Reference: Pipelined and Parallel Table Functions

This chapter describes the routines that need to be implemented to define pipelined and parallel table functions in C.

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ODCITableStart

Syntax

STATIC FUNCTION ODCITableStart(sctx OUT <imptype>, <args>) RETURN NUMBER

Purpose

ODCITableStart initializes the scan of a table function.

Table 20-1 ODCITableStart Parameters

Parameter	Meaning
sctx (OUT)	The scan context returned by this routine. This value is passed in as a parameter to the later scan routines. The scan context is an instance of the object type containing the implementation of the ODCITable routines.
args (IN)	Set of zero or more arguments specified by the user for the table function

Returns

ODCIConst.Success on success, ODCIConst.Error otherwise.

Usage Notes

• This is the first routine that is invoked to begin retrieving rows from a table function. This routine typically performs the setup needed for the scan. The scan context is created (as an object instance sctx) and returned to Oracle. The arguments to the table function, specified by the user in the SELECT statement, are passed in as parameters to this routine.
• Any REF CURSOR arguments of the table function must be declared as SYS_REFCURSOR type in the declaration of the ODCITableStart method.

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ODCITableFetch

Syntax

MEMBER FUNCTION ODCITableFetch(self IN OUT <imptype>, nrows IN NUMBER, rws OUT <coll-type>) RETURN NUMBER

Purpose

ODCITableFetch returns the next batch of rows from a table function.

Table 20-2 ODCITableFetch Parameters

Parameter	Meaning
self (IN)	The current scan context. This is the object instance returned to Oracle by the previous invocation of the scan routine.
self (OUT)	The scan context to be passed to later scan routine invocations.
nrows (IN)	The number of rows the system expects in the current fetch cycle. The method can ignore this value and return a different number of rows. If fewer rows are returned, the method is called again; if more rows are returned, they are processed in the next cycle.
rws (OUT)	The next batch of rows from the table function. This is returned as an instance of the same collection type as the return type of the table function.

Returns

ODCIConst.Success on success, ODCIConst.Error otherwise.

Usage Notes

ODCITableFetch is invoked one or more times by Oracle to retrieve all the rows in the collection returned by the table function. The scan context is passed in as a parameter. Typically ODCITableFetch uses the input scan context and computes the next set of rows to be returned to Oracle. In addition, it may update the scan context accordingly.

Returning more rows in each invocation of fetch() reduces the number of fetch calls that need to be made and thus improves performance.

Oracle calls ODCITableFetch repeatedly until all rows in the table function's collection have been returned. When all rows have been returned, ODCITableFetch should return a null collection.

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ODCITableClose

Syntax

MEMBER FUNCTION ODCITableClose(self IN <imptype>) RETURN NUMBER

Purpose

ODCITableClose performs cleanup operations after scanning a table function.

Table 20-3 ODCITableClose Parameters

Parameter	Meaning
self (IN)	The scan context set up by previous scan routine invocation

Returns

ODCIConst.Success on success, ODCIConst.Error otherwise.

Usage Notes

Oracle invokes ODCITableClose after the last fetch call. The scan context is passed in as a parameter. ODCITableClose then performs any necessary cleanup operations, such as freeing memory.

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ODCITableDescribe

Syntax

STATIC FUNCTION ODCITableDescribe(rtype OUT ANYTYPE, <args>) RETURN NUMBER

Purpose

ODCITableDescribe returns describe information for a table function whose return type is ANYDATASET.

Table 20-4 ODCITableDescribe Parameters

Parameter	Meaning
rtype (OUT)	The AnyType value that describes the returned rows from the table function
args (IN)	The set of zero or more arguments specified by the user for the table function.

Returns

ODCIConst.Success on success, ODCIConst.Error otherwise.

Usage Notes

Oracle invokes ODCITableDescribe at query compilation time to retrieve the specific type information.

Note that this interface is applicable only for table functions whose return type is ANYDATASET. The format of elements within the returned collection is conveyed to Oracle by returning an instance of ANYTYPE. The ANYTYPE instance specifies the actual structure of the returned rows in the context of the specific query.

ANYTYPE provides a datatype to model the metadata of a row--the names and datatypes of all the columns (fields) comprising the row. It also provides a set of PL/SQL and C interfaces for users to construct and access the metadata information. ANYDATASET, like ANYTYPE, contains a description of a given type, but ANYDATASET also contains a set of data instances of that type

The following example shows a query on a table function that uses the ANYDATASET type:

SELECT * FROM 
TABLE(CAST(AnyBooks('http://.../books.xml') AS ANYDATASET));

At query compilation time, Oracle invokes the ODCITableDescribe routine. The routine typically uses the user arguments to figure out the nature of the return rows. In this example, ODCITableDescribe consults the DTD of the XML documents at the specified location to determine the appropriate ANYTYPE value to return. Each ANYTYPE instance is constructed by invoking the constructor APIs with this field name and datatype information.

Any arguments of the table function which are not constants are passed to ODCITableDescribe as NULLs because their values are not known at compile time.