From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] "op must return bool to be used with subquery"? |
Date: | 1999-05-10 16:44:37 |
Message-ID: | 7679.926354677@sss.pgh.pa.us |
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Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
>> Given
>> create table t1 (name text, value float8);
>>
>> this fails:
>> SELECT name, value FROM t1 as touter WHERE
>> (value/(SELECT AVG(value) FROM t1 WHERE name = touter.name)) > 0.75;
>> ERROR: parser: '/' must return 'bool' to be used with subquery
> Aren't you really saying WHERE col / (subselect). That doesn't return
> bool, so the message seems correct.
No, look again: the result of the subselect is being used as an operand
within the WHERE clause:
WHERE (value/(SUBSELECT)) > 0.75;
If the / were the toplevel operator in the WHERE then the message would
make sense, because the WHERE clause as a whole must yield boolean.
But that doesn't mean that the operator immediately above the subselect
must yield boolean.
Besides, I already fixed this ;-)
> We don't allow subselects in target lists, or inside expressions.
We don't allow 'em in target lists, I think (anyone understand why not?)
but they work fine inside expressions in WHERE or HAVING.
regards, tom lane
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