Обсуждение:

I would like clarification on the first paragraph of section 9.20.2 on
the page at

      http://www.postgresql.org/docs/9.1/static/functions-subquery.html

regarding the syntax of the 'expression in (subquery)' clause.

What is meant by

     The right-hand side is a parenthesized subquery, which must return
     exactly one column.

?  Appears to me that the subquery must only contain the same number of
columns as the left hand side, not just 1 column.

thanks-j

well, it seems to me that section 9.20.2 makes sense.
http://www.w3schools.com/sql/sql_in.asp
I am not sure that you can compare multiple columns such as in:

SELECT * FROM Persons WHERE LastName, FirstName IN (SELECT LastName, FirstName FROM OtherPersons);

if this is what you mean, at least not using this method, which returns an error.

d

Le 15/11/11 18:29, jmscott@setspace.com a écrit :

I would like clarification on the first paragraph of section 9.20.2 on
the page at
     http://www.postgresql.org/docs/9.1/static/functions-subquery.html

regarding the syntax of the 'expression in (subquery)' clause.

What is meant by
    The right-hand side is a parenthesized subquery, which must return    exactly one column.

?  Appears to me that the subquery must only contain the same number of
columns as the left hand side, not just 1 column.

thanks-j

here is a trivial example in 9.1

    jmscott=> select (1, 2) in (select 1, 2);
 ?column?
----------
 t
(1 row)

where the right hand side returns 2 columns, not exactly one column,
contradicting what the docs say:

>>       The right-hand side is a parenthesized subquery, which must return
>>       exactly one column.

seems like a documentation error.  what am i missing?

-j

> well, it seems to me that section 9.20.2 makes sense.
> http://www.w3schools.com/sql/sql_in.asp
> I am not sure that you can compare multiple columns such as in:
>
> SELECT * FROM Persons WHERE LastName, FirstName IN (SELECT LastName,
> FirstName FROM OtherPersons);
>
> if this is what you mean, at least not using this method, which returns
> an error.
>
> d
>
> Le 15/11/11 18:29, jmscott@setspace.com a écrit :
>> I would like clarification on the first paragraph of section 9.20.2 on
>> the page at
>>
>>        http://www.postgresql.org/docs/9.1/static/functions-subquery.html
>>
>> regarding the syntax of the 'expression in (subquery)' clause.
>>
>> What is meant by
>>
>>       The right-hand side is a parenthesized subquery, which must return
>>       exactly one column.
>>
>> ?  Appears to me that the subquery must only contain the same number of
>> columns as the left hand side, not just 1 column.
>>
>> thanks-j
>>
>>
>
>
>

Right, I am probably wrong. Some other opinion?

d


Le 15/11/11 19:48, jmscott@setspace.com a écrit :

here is a trivial example in 9.1
   jmscott=> select (1, 2) in (select 1, 2);?column?
----------t
(1 row)

where the right hand side returns 2 columns, not exactly one column,
contradicting what the docs say:

      The right-hand side is a parenthesized subquery, which must return     exactly one column.

seems like a documentation error.  what am i missing?

-j

well, it seems to me that section 9.20.2 makes sense.
http://www.w3schools.com/sql/sql_in.asp
I am not sure that you can compare multiple columns such as in:

SELECT * FROM Persons WHERE LastName, FirstName IN (SELECT LastName,
FirstName FROM OtherPersons);

if this is what you mean, at least not using this method, which returns
an error.

d

Le 15/11/11 18:29, jmscott@setspace.com a écrit :

I would like clarification on the first paragraph of section 9.20.2 on
the page at
      http://www.postgresql.org/docs/9.1/static/functions-subquery.html

regarding the syntax of the 'expression in (subquery)' clause.

What is meant by
     The right-hand side is a parenthesized subquery, which must return     exactly one column.

?  Appears to me that the subquery must only contain the same number of
columns as the left hand side, not just 1 column.

thanks-j