Lincoln Yeoh wrote:
> Hi everyone,
>
> say I have a table test
> create table test (a int, b text);
>
> and I want to ensure that 'b' is unique for a particular 'a' ('a' not being
> unique).
>
> Right now I can do something like
> begin transaction
> select count(*) from test where b =$value;
> if count = 0 then insert into test (a,b) values ($a, $value);
>
> But there is still a chance of a duplicate being inserted.
use unique constraint on column a as in:
CREATE TABLE test (a char unique, b int);
José