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doc: clarify aliasing of VALUES in FROM clauses

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The VALUES reference page said that an AS clause was required when
VALUES is used in a FROM clause. This was imprecise because AS is
optional when specifying an alias.

In v14 and v15, a table alias is still required in this case, so state
that explicitly instead. In v16 and later, commit bcedd8f5fc made table
aliases for subqueries in FROM clauses optional, so state that the
table alias is optional there. In all branches, continue to recommend
explicit column aliases as good practice.

Backpatch to all supported versions.

Author: Ian Barwick <barwick@gmail.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CAB8KJ=jrvZdNLLhYSiCgbjLTz2LKEjYw+-HVQkaF+kgk61KtHA@mail.gmail.com
Backpatch-through: 14
This commit is contained in:
Fujii Masao
2026-09-01 22:46:10 +09:00
parent bfb08d0946
commit 4aa640a395
1 changed files with 3 additions and 4 deletions
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7
doc/src/sgml/ref/values.sgml
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@@ -198,10 +198,9 @@ UPDATE employees SET salary = salary * v.increase
WHERE employees.depno = v.depno AND employees.sales &gt;= v.target;
</programlisting>
Note that an <literal>AS</literal> clause is required when <command>VALUES</command>
is used in a <literal>FROM</literal> clause, just as is true for
<command>SELECT</command>. It is not required that the <literal>AS</literal> clause
specify names for all the columns, but it's good practice to do so.
Note that if <command>VALUES</command> is used in a <literal>FROM</literal>
clause, a table alias is optional. Assigning alias names to the columns
of the <command>VALUES</command> list is optional, but is good practice.
(The default column names for <command>VALUES</command> are <literal>column1</literal>,
<literal>column2</literal>, etc. in <productname>PostgreSQL</productname>, but
these names might be different in other database systems.)