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Commit1da162e

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Fix SQL:2008 FETCH FIRST syntax to allow parameters.
OFFSET <x> ROWS FETCH FIRST <y> ROWS ONLY syntax is supposed to accept<simple value specification>, which includes parameters as well asliterals. When this syntax was added all those years ago, it was doneinconsistently, with <x> and <y> being different subsets of thestandard syntax.Rectify that by making <x> and <y> accept the same thing, and allowingeither a (signed) numeric literal or a c_expr there, which allows forparameters, variables, and parenthesized arbitrary expressions.Per bug #15200 from Lukas Eder.Backpatch all the way, since this has been broken from the start.Discussion:https://postgr.es/m/877enz476l.fsf@news-spur.riddles.org.ukDiscussion:http://postgr.es/m/152647780335.27204.16895288237122418685@wrigleys.postgresql.org
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2 files changed

+39
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2 files changed

+39
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lines changed

‎doc/src/sgml/ref/select.sgml

Lines changed: 6 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1399,10 +1399,12 @@ OFFSET <replaceable class="parameter">start</replaceable>
13991399
OFFSET <replaceable class="parameter">start</replaceable> { ROW | ROWS }
14001400
FETCH { FIRST | NEXT } [ <replaceable class="parameter">count</replaceable> ] { ROW | ROWS } ONLY
14011401
</synopsis>
1402-
In this syntax, to write anything except a simple integer constant for
1403-
<replaceable class="parameter">start</replaceable> or <replaceable
1404-
class="parameter">count</replaceable>, you must write parentheses
1405-
around it.
1402+
In this syntax, the <replaceable class="parameter">start</replaceable>
1403+
or <replaceable class="parameter">count</replaceable> value is required by
1404+
the standard to be a literal constant, a parameter, or a variable name;
1405+
as a <productname>PostgreSQL</productname> extension, other expressions
1406+
are allowed, but will generally need to be enclosed in parentheses to avoid
1407+
ambiguity.
14061408
If <replaceable class="parameter">count</replaceable> is
14071409
omitted in a <literal>FETCH</literal> clause, it defaults to 1.
14081410
<literal>ROW</literal>

‎src/backend/parser/gram.y

Lines changed: 33 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -451,7 +451,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
451451

452452
%type<node>fetch_argslimit_clauseselect_limit_value
453453
offset_clauseselect_offset_value
454-
select_offset_value2opt_select_fetch_first_value
454+
select_fetch_first_valueI_or_F_const
455455
%type<ival>row_or_rowsfirst_or_next
456456

457457
%type<list>OptSeqOptListSeqOptListOptParenthesizedSeqOptList
@@ -11570,15 +11570,23 @@ limit_clause:
1157011570
parser_errposition(@1)));
1157111571
}
1157211572
/* SQL:2008 syntax*/
11573-
|FETCHfirst_or_nextopt_select_fetch_first_valuerow_or_rowsONLY
11573+
/* to avoid shift/reduce conflicts, handle the optional value with
11574+
* a separate production rather than an opt_ expression. The fact
11575+
* that ONLY is fully reserved means that this way, we defer any
11576+
* decision about what rule reduces ROW or ROWS to the point where
11577+
* we can see the ONLY token in the lookahead slot.
11578+
*/
11579+
|FETCHfirst_or_nextselect_fetch_first_valuerow_or_rowsONLY
1157411580
{$$ =$3; }
11581+
|FETCHfirst_or_nextrow_or_rowsONLY
11582+
{$$ = makeIntConst(1, -1); }
1157511583
;
1157611584

1157711585
offset_clause:
1157811586
OFFSETselect_offset_value
1157911587
{$$ =$2; }
1158011588
/* SQL:2008 syntax*/
11581-
|OFFSETselect_offset_value2row_or_rows
11589+
|OFFSETselect_fetch_first_valuerow_or_rows
1158211590
{$$ =$2; }
1158311591
;
1158411592

@@ -11597,22 +11605,31 @@ select_offset_value:
1159711605

1159811606
/*
1159911607
* Allowing full expressions without parentheses causes various parsing
11600-
* problems with the trailing ROW/ROWS key words. SQL only calls for
11601-
* constants, so we allow the rest only with parentheses. If omitted,
11602-
* default to 1.
11608+
* problems with the trailing ROW/ROWS key words. SQL spec only calls for
11609+
* <simple value specification>, which is either a literal or a parameter (but
11610+
* an <SQL parameter reference> could be an identifier, bringing up conflicts
11611+
* with ROW/ROWS). We solve this by leveraging the presence of ONLY (see above)
11612+
* to determine whether the expression is missing rather than trying to make it
11613+
* optional in this rule.
11614+
*
11615+
* c_expr covers almost all the spec-required cases (and more), but it doesn't
11616+
* cover signed numeric literals, which are allowed by the spec. So we include
11617+
* those here explicitly. We need FCONST as well as ICONST because values that
11618+
* don't fit in the platform's "long", but do fit in bigint, should still be
11619+
* accepted here. (This is possible in 64-bit Windows as well as all 32-bit
11620+
* builds.)
1160311621
*/
11604-
opt_select_fetch_first_value:
11605-
SignedIconst{$$ = makeIntConst($1,@1); }
11606-
|'('a_expr')'{$$ =$2; }
11607-
|/*EMPTY*/{$$ = makeIntConst(1, -1); }
11622+
select_fetch_first_value:
11623+
c_expr{$$ =$1; }
11624+
|'+'I_or_F_const
11625+
{$$ = (Node *) makeSimpleA_Expr(AEXPR_OP,"+",NULL,$2,@1); }
11626+
|'-'I_or_F_const
11627+
{$$ = doNegate($2,@1); }
1160811628
;
1160911629

11610-
/*
11611-
* Again, the trailing ROW/ROWS in this case prevent the full expression
11612-
* syntax. c_expr is the best we can do.
11613-
*/
11614-
select_offset_value2:
11615-
c_expr{$$ =$1; }
11630+
I_or_F_const:
11631+
Iconst{$$ = makeIntConst($1,@1); }
11632+
|FCONST{$$ = makeFloatConst($1,@1); }
1161611633
;
1161711634

1161811635
/* noise words*/

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