On 16-11-2013 12:52, liviuslivius wrote:
> Hi,
> many times i need to return more then one field from subquery
> but this is not possible and then i must do some join and group by or
> write stored proc or other trick like concat fields by "||"
> My question is "Is this because of SQL standard or this is not simple to
> develop?"
The SQL Standard allows for it:
<query specification> ::=
SELECT [ <set quantifier> ] <select list> <table expression>
<select list> ::=
...
| <select sublist> [ { <comma> <select sublist> }... ]
<select sublist> ::=
<derived column>
...
<derived column> ::=
<value expression> [ <as clause> ]
<value expression> ::=
...
| <row value expression>
<row value expression> ::=
...
| <explicit row value constructor>
<explicit row value constructor> ::=
...
| <row subquery>
<row subquery> ::=
<subquery>
<subquery> ::=
<left paren> <query expression> <right paren>
<query expression> ::=
[ <with clause> ] <query expression body>
[ <order by clause> ] [ <result offset clause> ] [ <fetch first clause> ]
<query expression body> ::=
<query term>
...
<query term> ::=
<query primary>
<query primary> ::=
<simple table>
...
<simple table> ::=
<query specification>
...
And <query specification> is already defined at the top.
Row value constructors would be very nice to have, but the full breadth
of features this allows (including things like (field1, field2) = (1,
2), or (2, 3) < (3,4)) will probably take a lot of work.
Personally I'd like to have this, but then I'd also like to have table
value constructors :)
Mark
--
Mark Rotteveel
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