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Support multi-argument UNNEST(), and TABLE() syntax for multiple functions.

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This patch adds the ability to write TABLE( function1(), function2(), ...)
as a single FROM-clause entry.  The result is the concatenation of the
first row from each function, followed by the second row from each
function, etc; with NULLs inserted if any function produces fewer rows than
others.  This is believed to be a much more useful behavior than what
Postgres currently does with multiple SRFs in a SELECT list.

This syntax also provides a reasonable way to combine use of column
definition lists with WITH ORDINALITY: put the column definition list
inside TABLE(), where it's clear that it doesn't control the ordinality
column as well.

Also implement SQL-compliant multiple-argument UNNEST(), by turning
UNNEST(a,b,c) into TABLE(unnest(a), unnest(b), unnest(c)).

The SQL standard specifies TABLE() with only a single function, not
multiple functions, and it seems to require an implicit UNNEST() which is
not what this patch does.  There may be something wrong with that reading
of the spec, though, because if it's right then the spec's TABLE() is just
a pointless alternative spelling of UNNEST().  After further review of
that, we might choose to adopt a different syntax for what this patch does,
but in any case this functionality seems clearly worthwhile.

Andrew Gierth, reviewed by Zoltán Böszörményi and Heikki Linnakangas, and
significantly revised by me
This commit is contained in:
Tom Lane
2013-11-21 19:37:02 -05:00
parent 38f4328981
commit 784e762e88
48 changed files with 2643 additions and 1207 deletions
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26
src/include/nodes/execnodes.h
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@@ -1395,24 +1395,26 @@ typedef struct SubqueryScanState
* function appearing in FROM (typically a function returning set).
*
* eflags node's capability flags
* ordinal column value for WITH ORDINALITY
* scan_tupdesc scan tuple descriptor
* func_tupdesc function tuple descriptor
* func_slot function result slot, or null
* tuplestorestate private state of tuplestore.c
* funcexpr state for function expression being evaluated
* ordinality is this scan WITH ORDINALITY?
* simple true if we have 1 function and no ordinality
* ordinal current ordinal column value
* nfuncs number of functions being executed
* funcstates per-function execution states (private in
* nodeFunctionscan.c)
* ----------------
*/
struct FunctionScanPerFuncState;
typedef struct FunctionScanState
{
ScanState ss; /* its first field is NodeTag */
int eflags;
int64 ordinal;
TupleDesc scan_tupdesc;
TupleDesc func_tupdesc;
TupleTableSlot *func_slot;
Tuplestorestate *tuplestorestate;
ExprState *funcexpr;
bool ordinality;
bool simple;
int64 ordinal;
int nfuncs;
struct FunctionScanPerFuncState *funcstates; /* array of length
* nfuncs */
} FunctionScanState;
/* ----------------