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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 as
literals. When this syntax was added all those years ago, it was done
inconsistently, with <x> and <y> being different subsets of the
standard syntax.

Rectify that by making <x> and <y> accept the same thing, and allowing
either a (signed) numeric literal or a c_expr there, which allows for
parameters, 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.uk
Discussion: http://postgr.es/m/152647780335.27204.16895288237122418685@wrigleys.postgresql.org
This commit is contained in:
Andrew Gierth 2018-05-21 17:02:17 +01:00
parent 806d08c048
commit 1da162e1f5
2 changed files with 39 additions and 20 deletions
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10
doc/src/sgml/ref/select.sgml
View File

@ -1399,10 +1399,12 @@ OFFSET <replaceable class="parameter">start</replaceable>
OFFSET <replaceable class="parameter">start</replaceable> { ROW | ROWS }
FETCH { FIRST | NEXT } [ <replaceable class="parameter">count</replaceable> ] { ROW | ROWS } ONLY
</synopsis>
In this syntax, to write anything except a simple integer constant for
<replaceable class="parameter">start</replaceable> or <replaceable
class="parameter">count</replaceable>, you must write parentheses
around it.
In this syntax, the <replaceable class="parameter">start</replaceable>
or <replaceable class="parameter">count</replaceable> value is required by
the standard to be a literal constant, a parameter, or a variable name;
as a <productname>PostgreSQL</productname> extension, other expressions
are allowed, but will generally need to be enclosed in parentheses to avoid
ambiguity.
If <replaceable class="parameter">count</replaceable> is
omitted in a <literal>FETCH</literal> clause, it defaults to 1.
<literal>ROW</literal>

49
src/backend/parser/gram.y
View File

@ -451,7 +451,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
%type <node> fetch_args limit_clause select_limit_value
offset_clause select_offset_value
select_offset_value2 opt_select_fetch_first_value
select_fetch_first_value I_or_F_const
%type <ival> row_or_rows first_or_next
%type <list> OptSeqOptList SeqOptList OptParenthesizedSeqOptList
@ -11570,15 +11570,23 @@ limit_clause:
parser_errposition(@1)));
}
/* SQL:2008 syntax */
| FETCH first_or_next opt_select_fetch_first_value row_or_rows ONLY
/* to avoid shift/reduce conflicts, handle the optional value with
* a separate production rather than an opt_ expression. The fact
* that ONLY is fully reserved means that this way, we defer any
* decision about what rule reduces ROW or ROWS to the point where
* we can see the ONLY token in the lookahead slot.
*/
| FETCH first_or_next select_fetch_first_value row_or_rows ONLY
{ $$ = $3; }
| FETCH first_or_next row_or_rows ONLY
{ $$ = makeIntConst(1, -1); }
;
offset_clause:
OFFSET select_offset_value
{ $$ = $2; }
/* SQL:2008 syntax */
| OFFSET select_offset_value2 row_or_rows
| OFFSET select_fetch_first_value row_or_rows
{ $$ = $2; }
;
@ -11597,22 +11605,31 @@ select_offset_value:
/*
* Allowing full expressions without parentheses causes various parsing
* problems with the trailing ROW/ROWS key words. SQL only calls for
* constants, so we allow the rest only with parentheses. If omitted,
* default to 1.
* problems with the trailing ROW/ROWS key words. SQL spec only calls for
* <simple value specification>, which is either a literal or a parameter (but
* an <SQL parameter reference> could be an identifier, bringing up conflicts
* with ROW/ROWS). We solve this by leveraging the presence of ONLY (see above)
* to determine whether the expression is missing rather than trying to make it
* optional in this rule.
*
* c_expr covers almost all the spec-required cases (and more), but it doesn't
* cover signed numeric literals, which are allowed by the spec. So we include
* those here explicitly. We need FCONST as well as ICONST because values that
* don't fit in the platform's "long", but do fit in bigint, should still be
* accepted here. (This is possible in 64-bit Windows as well as all 32-bit
* builds.)
*/
opt_select_fetch_first_value:
SignedIconst { $$ = makeIntConst($1, @1); }
| '(' a_expr ')' { $$ = $2; }
| /*EMPTY*/ { $$ = makeIntConst(1, -1); }
select_fetch_first_value:
c_expr { $$ = $1; }
| '+' I_or_F_const
{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "+", NULL, $2, @1); }
| '-' I_or_F_const
{ $$ = doNegate($2, @1); }
;
/*
* Again, the trailing ROW/ROWS in this case prevent the full expression
* syntax. c_expr is the best we can do.
*/
select_offset_value2:
c_expr { $$ = $1; }
I_or_F_const:
Iconst { $$ = makeIntConst($1,@1); }
| FCONST { $$ = makeFloatConst($1,@1); }
;
/* noise words */