@ -44,30 +44,34 @@
* is used to run finalize functions and compute the output tuple ;
* this context can be reset once per output tuple .
*
* Beginning in PostgreSQL 8.1 , the executor ' s AggState node is passed as
* the fmgr " context " value in all transfunc and finalfunc calls . It is
* not really intended that the transition functions will look into the
* AggState node , but they can use code like
* if ( fcinfo - > context & & IsA ( fcinfo - > context , AggState ) )
* to verify that they are being called by nodeAgg . c and not as ordinary
* SQL functions . The main reason a transition function might want to know
* that is that it can avoid palloc ' ing a fixed - size pass - by - ref transition
* value on every call : it can instead just scribble on and return its left
* input . Ordinarily it is completely forbidden for functions to modify
* pass - by - ref inputs , but in the aggregate case we know the left input is
* either the initial transition value or a previous function result , and
* in either case its value need not be preserved . See int8inc ( ) for an
* example . Notice that advance_transition_function ( ) is coded to avoid a
* data copy step when the previous transition value pointer is returned .
* Also , some transition functions make use of the aggcontext to store
* working state .
* The executor ' s AggState node is passed as the fmgr " context " value in
* all transfunc and finalfunc calls . It is not recommended that the
* transition functions look at the AggState node directly , but they can
* use AggCheckCallContext ( ) to verify that they are being called by
* nodeAgg . c ( and not as ordinary SQL functions ) . The main reason a
* transition function might want to know this is so that it can avoid
* palloc ' ing a fixed - size pass - by - ref transition value on every call :
* it can instead just scribble on and return its left input . Ordinarily
* it is completely forbidden for functions to modify pass - by - ref inputs ,
* but in the aggregate case we know the left input is either the initial
* transition value or a previous function result , and in either case its
* value need not be preserved . See int8inc ( ) for an example . Notice that
* advance_transition_function ( ) is coded to avoid a data copy step when
* the previous transition value pointer is returned . Also , some
* transition functions want to store working state in addition to the
* nominal transition value ; they can use the memory context returned by
* AggCheckCallContext ( ) to do that .
*
* Note : AggCheckCallContext ( ) is available as of PostgreSQL 9.0 . The
* AggState is available as context in earlier releases ( back to 8.1 ) ,
* but direct examination of the node is needed to use it before 9.0 .
*
*
* Portions Copyright ( c ) 1996 - 2010 , PostgreSQL Global Development Group
* Portions Copyright ( c ) 1994 , Regents of the University of California
*
* IDENTIFICATION
* $ PostgreSQL : pgsql / src / backend / executor / nodeAgg . c , v 1.171 2010 / 01 / 02 16 : 57 : 41 momjian Exp $
* $ PostgreSQL : pgsql / src / backend / executor / nodeAgg . c , v 1.172 2010 / 02 / 08 20 : 39 : 51 tgl Exp $
*
* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
*/
@ -1969,6 +1973,42 @@ ExecReScanAgg(AggState *node, ExprContext *exprCtxt)
ExecReScan ( ( ( PlanState * ) node ) - > lefttree , exprCtxt ) ;
}
/*
* AggCheckCallContext - test if a SQL function is being called as an aggregate
*
* The transition and / or final functions of an aggregate may want to verify
* that they are being called as aggregates , rather than as plain SQL
* functions . They should use this function to do so . The return value
* is nonzero if being called as an aggregate , or zero if not . ( Specific
* nonzero values are AGG_CONTEXT_AGGREGATE or AGG_CONTEXT_WINDOW , but more
* values could conceivably appear in future . )
*
* If aggcontext isn ' t NULL , the function also stores at * aggcontext the
* identity of the memory context that aggregate transition values are
* being stored in .
*/
int
AggCheckCallContext ( FunctionCallInfo fcinfo , MemoryContext * aggcontext )
{
if ( fcinfo - > context & & IsA ( fcinfo - > context , AggState ) )
{
if ( aggcontext )
* aggcontext = ( ( AggState * ) fcinfo - > context ) - > aggcontext ;
return AGG_CONTEXT_AGGREGATE ;
}
if ( fcinfo - > context & & IsA ( fcinfo - > context , WindowAggState ) )
{
if ( aggcontext )
* aggcontext = ( ( WindowAggState * ) fcinfo - > context ) - > wincontext ;
return AGG_CONTEXT_WINDOW ;
}
/* this is just to prevent "uninitialized variable" warnings */
if ( aggcontext )
* aggcontext = NULL ;
return 0 ;
}
/*
* aggregate_dummy - dummy execution routine for aggregate functions
*
Tom Lane
16 years ago