Re: SELECT Question

Jeffrey,
second solution is a beauty... thanks a lot.

Alex

Jeffrey Melloy wrote:

> If I'm understanding you correctly, you can do something like:
>
> select cola,
>             colb,
>             exists
>                  (select 'x'
>                   from tableb
>                   where colc = colb)
> from tablea
>
> Since that has a subselect, you may get better performance with
> something like this:
> select   cola,
>              colb,
>             case when colc is null
>                  then 'f' else 't' end as exists
> from table1 left join table2 on colb = colc;
>
> jmelloy=# create table table1(cola serial, colb char);
> NOTICE:  CREATE TABLE will create implicit sequence 'table1_cola_seq'
> for SERIAL column 'table1.cola'
> CREATE TABLE
> jmelloy=# create table table2 (colc char);
> CREATE TABLE
> jmelloy=# insert into table1 (colb) values ('A');
> INSERT 1551538 1
> jmelloy=# insert into table1 (colb) values ('B');
> INSERT 1551539 1
> jmelloy=# insert into table1 (colb) values ('a');
> INSERT 1551540 1
> jmelloy=# insert into table2 values ('B');
> INSERT 1551541 1
> jmelloy=# select cola, colb, exists (select 'x' from table2 where colc
> = colb) from table1;
>  cola | colb | ?column?
> ------+------+----------
>     1 | A    | f
>     2 | B    | t
>     3 | a    | f
> (3 rows)
> jmelloy=# select cola, colb, case when colc is null then 'f' else 't'
> end as exists from table1 left join table2 on colb = colc;
>  cola | colb | exists
> ------+------+--------
>     1 | A    | f
>     2 | B    | t
>     3 | a    | f
> (3 rows)
> On Sunday, August 31, 2003, at 12:03  PM, Alex wrote:
>
>> Hi,
>>
>> I need to form a query where i can add some columns based on the result.
>>
>>
>> Table A
>> ColA, ColB
>> ----------
>> 1      A
>> 2      B
>> 3      A
>>
>> Table B
>> ColC
>> ----
>> A
>>
>> If A exists if would like the result back as
>> 1  A   OK
>> 2  B   NG
>> 3  A   OK
>>
>> Is it possible to replace the value in the query ?
>>
>> Thanks
>> Alex
>>
>>
>>
>>
>>
>>
>>
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>
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