Re: Query will execute when inner query have issue

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: selva kumar <selva(dot)logic(at)hotmail(dot)com>
Cc: "pgsql-bugs(at)lists(dot)postgresql(dot)org" <pgsql-bugs(at)lists(dot)postgresql(dot)org>
Subject: Re: Query will execute when inner query have issue
Date: 2020-01-23 14:43:33
Message-ID: 5259.1579790613@sss.pgh.pa.us
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selva kumar <selva(dot)logic(at)hotmail(dot)com> writes:
> We tried query in a following manner.
> SELECT * FROM A where A.id IN (SELECT B.id from B);
> In the above query Table B does not have id. But this query return all A table records

You sure that's *actually* what you wrote? The usual mistake is to
fail to qualify the inner query's column reference at all:

SELECT * FROM A where A.id IN (SELECT id from B);

If B has no "id" column, it's still a legal SQL query, interpreted as

SELECT * FROM A where A.id IN (SELECT A.id from B);

so as long as B has any rows, the IN-test succeeds for every non-null
value of A.id. People get burned by that all the time, but it's
acting as required by the SQL standard.

regards, tom lane

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