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Add IGNORE NULLS/RESPECT NULLS option to Window functions.

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Add IGNORE NULLS/RESPECT NULLS option (null treatment clause) to lead,
lag, first_value, last_value and nth_value window functions.  If
unspecified, the default is RESPECT NULLS which includes NULL values
in any result calculation. IGNORE NULLS ignores NULL values.

Built-in window functions are modified to call new API
WinCheckAndInitializeNullTreatment() to indicate whether they accept
IGNORE NULLS/RESPECT NULLS option or not (the API can be called by
user defined window functions as well).  If WinGetFuncArgInPartition's
allowNullTreatment argument is true and IGNORE NULLS option is given,
WinGetFuncArgInPartition() or WinGetFuncArgInFrame() will return
evaluated function's argument expression on specified non NULL row (if
it exists) in the partition or the frame.

When IGNORE NULLS option is given, window functions need to visit and
evaluate same rows over and over again to look for non null rows. To
mitigate the issue, 2-bit not null information array is created while
executing window functions to remember whether the row has been
already evaluated to NULL or NOT NULL. If already evaluated, we could
skip the evaluation work, thus we could get better performance.

Author: Oliver Ford <ojford@gmail.com>
Co-authored-by: Tatsuo Ishii <ishii@postgresql.org>
Reviewed-by: Krasiyan Andreev <krasiyan@gmail.com>
Reviewed-by: Andrew Gierth <andrew@tao11.riddles.org.uk>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: David Fetter <david@fetter.org>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: "David G. Johnston" <david.g.johnston@gmail.com>
Reviewed-by: Chao Li <lic@highgo.com>
Discussion: https://postgr.es/m/flat/CAGMVOdsbtRwE_4+v8zjH1d9xfovDeQAGLkP_B6k69_VoFEgX-A@mail.gmail.com
This commit is contained in:
Tatsuo Ishii
2025-10-03 09:47:36 +09:00
parent 381f5cffae
commit 25a30bbd42
15 changed files with 1092 additions and 61 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
src/backend/utils/adt/ruleutils.c
View File

@@ -11091,7 +11091,12 @@ get_windowfunc_expr_helper(WindowFunc *wfunc, deparse_context *context,
get_rule_expr((Node *) wfunc->aggfilter, context, false);
}
appendStringInfoString(buf, ") OVER ");
appendStringInfoString(buf, ") ");
if (wfunc->ignore_nulls == PARSER_IGNORE_NULLS)
appendStringInfoString(buf, "IGNORE NULLS ");
appendStringInfoString(buf, "OVER ");
if (context->windowClause)
{

10
src/backend/utils/adt/windowfuncs.c
View File

@@ -86,6 +86,7 @@ window_row_number(PG_FUNCTION_ARGS)
WindowObject winobj = PG_WINDOW_OBJECT();
int64 curpos = WinGetCurrentPosition(winobj);
WinCheckAndInitializeNullTreatment(winobj, false, fcinfo);
WinSetMarkPosition(winobj, curpos);
PG_RETURN_INT64(curpos + 1);
}
@@ -141,6 +142,7 @@ window_rank(PG_FUNCTION_ARGS)
rank_context *context;
bool up;
WinCheckAndInitializeNullTreatment(winobj, false, fcinfo);
up = rank_up(winobj);
context = (rank_context *)
WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
@@ -203,6 +205,7 @@ window_dense_rank(PG_FUNCTION_ARGS)
rank_context *context;
bool up;
WinCheckAndInitializeNullTreatment(winobj, false, fcinfo);
up = rank_up(winobj);
context = (rank_context *)
WinGetPartitionLocalMemory(winobj, sizeof(rank_context));
@@ -266,6 +269,7 @@ window_percent_rank(PG_FUNCTION_ARGS)
int64 totalrows = WinGetPartitionRowCount(winobj);
Assert(totalrows > 0);
WinCheckAndInitializeNullTreatment(winobj, false, fcinfo);
up = rank_up(winobj);
context = (rank_context *)
@@ -335,6 +339,7 @@ window_cume_dist(PG_FUNCTION_ARGS)
int64 totalrows = WinGetPartitionRowCount(winobj);
Assert(totalrows > 0);
WinCheckAndInitializeNullTreatment(winobj, false, fcinfo);
up = rank_up(winobj);
context = (rank_context *)
@@ -413,6 +418,7 @@ window_ntile(PG_FUNCTION_ARGS)
WindowObject winobj = PG_WINDOW_OBJECT();
ntile_context *context;
WinCheckAndInitializeNullTreatment(winobj, false, fcinfo);
context = (ntile_context *)
WinGetPartitionLocalMemory(winobj, sizeof(ntile_context));
@@ -535,6 +541,7 @@ leadlag_common(FunctionCallInfo fcinfo,
bool isnull;
bool isout;
WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
if (withoffset)
{
offset = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
@@ -652,6 +659,7 @@ window_first_value(PG_FUNCTION_ARGS)
Datum result;
bool isnull;
WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
result = WinGetFuncArgInFrame(winobj, 0,
0, WINDOW_SEEK_HEAD, true,
&isnull, NULL);
@@ -673,6 +681,7 @@ window_last_value(PG_FUNCTION_ARGS)
Datum result;
bool isnull;
WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
result = WinGetFuncArgInFrame(winobj, 0,
0, WINDOW_SEEK_TAIL, true,
&isnull, NULL);
@@ -696,6 +705,7 @@ window_nth_value(PG_FUNCTION_ARGS)
bool isnull;
int32 nth;
WinCheckAndInitializeNullTreatment(winobj, true, fcinfo);
nth = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
if (isnull)
PG_RETURN_NULL();