Re: SELECT Question

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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