Ambiguity in VALUES synopsis: LIMIT vs FETCH

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От Cheng Ding
Тема Ambiguity in VALUES synopsis: LIMIT vs FETCH
Дата
Msg-id CAMfZ+xO5hbrZJu46S5QYgAtDRBr-UXzR_8VOAraQQX+8_VasQg@mail.gmail.com
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Ответы Re: Ambiguity in VALUES synopsis: LIMIT vs FETCH
Список pgsql-docs

Hello docs team,

I believe there’s an ambiguity in the VALUES command synopsis that can mislead readers into thinking LIMIT and FETCH can be used together.

What I ran

VALUES (12, 'nectarine') LIMIT 1 FETCH FIRST 1 ROW ONLY;

What happened

ERROR: syntax error at or near "FETCH"

Why I think the docs are ambiguous

The current synopsis for VALUES shows:

VALUES ( expression [, ...] ) [, ...] [ ORDER BY sort_expression [ ASC | DESC | USING operator ] [, ...] ] [ LIMIT { count | ALL } ] [ OFFSET start [ ROW | ROWS ] ] [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]

As written, this looks like LIMIT … and FETCH … are independent optional clauses that could both appear. In practice (and in the underlying grammar), FETCH is the SQL-standard alternative to LIMIT; they are mutually exclusive.

Suggested fix (one option)

Adjust the synopsis to make the alternation explicit, for example:

[ { LIMIT { count | ALL } [ OFFSET start [ ROW | ROWS ] ] | [ OFFSET start [ ROW | ROWS ] ] FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY } ]

Alternatively, add a short note right under the synopsis:

Note: FETCH { FIRST | NEXT } … ONLY is an alternative to LIMIT and cannot be used together with it.

EnvironmentPostgreSQL v17.6

Best regards,
Cheng Ding
The University of Texas at Austin


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