23 Pipelined and Parallel Table Functions

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

This chapter contains this topic:

Routines for Pipelined and Parallel Table Functions in C

Routines for Pipelined and Parallel Table Functions in C

The following C methods, summarized in support parallel and pipelined table functions.

Table 23-1 Summary of Pipelined and Parallel Table Functions for C

Function	Description
ODCITableClose()	Performs cleanup operations after scanning a table function.
ODCITableDescribe()	Returns describe information for a table function whose return type is `ANYDATASET`.
ODCITableFetch()	returns the next batch of rows from a table function.
ODCITablePrepare()	Prepares the scan context and other query information at compile time.
ODCITableStart()	initializes the scan of a table function.

ODCITableClose()

ODCITableClose performs cleanup operations after scanning a table function.

Syntax

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

Parameter	In/Out	Description
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.
If ODCITablePrepare is implemented, this routine is only called once, at the end of query execution, rather than each time the table function exits.

ODCITableDescribe()

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

Syntax

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

Parameter	In/Out	Description
rtype	OUT	The `AnyType` value that describes the returned rows from the table function
args	IN	The set of zero or more user specified arguments for the table function.

Returns

ODCIConst.Success on success, ODCIConst.Error otherwise.

Usage Notes

If the optional routine ODCITableDescribe is implemented, Oracle invokes it at query compilation time to retrieve the specific type information.
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 that are not constants are passed to ODCITableDescribe as NULLs because their values are not known at compile time.

ODCITableFetch()

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

Syntax

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

Parameter	In/Out	Description
self	IN OUT	The in-bound is the scan context set up by previous scan routine invocation; the outbound is 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.

ODCITablePrepare()

Prepares the scan context and other query information at compile time.

Syntax

STATIC FUNCTION ODCITablePrepare(
   sctx OUT <imptype>, 
   tf_info SYS.ODCITabFuncInfo,
   args);

Parameter	In/Out	Description
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.
tf_info		Contains the projection information and the return type's table descriptor object (TDO): Attrs (`SYS.ODCINumberList`): lists the positions of the referenced attributes of the table function's output collection type RefType (`SYS.AnyType`): for `AnyDataSet` table functions, this is the actual return type expected to be returned in the `AnyDataSet` collection.
args	IN	The arguments that will be passed to the table function. This method is invoked at compile time; thus, only literal arguments have values. Column and expression arguments are passed as null values.

Usage Notes

This method prepares the scan context based on the information known at compile time. This scan context is passed to ODCITableStart when it is called at the beginning of query execution.
If this optional method is implemented, ODCITableClose is only called once at the end of query execution. Each time the table function is restarted, ODCITableStart is called and passed the scan context. This allows the table function to maintain context between restarts, and to perform cleanup operations only once at the end of query execution.

ODCITableStart()

ODCITableStart initializes the scan of a table function.

Syntax

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

Parameter	In/Out	Description
self	IN 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. If `ODCITablePrepare` is implemented, the scan context it creates is passed in to `ODCITableStart`.
args	IN	Set of zero or more arguments specified by the user for the table function
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

If ODCITablePrepare is not implemented, 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. If ODCITablePrepare is implemented, it creates the scan context at compile time, and that scan context is passed in 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.