> umm when i declare a unique constraint on 2 fields in a table like so
>
> unique (col1,col2),
>
> if i insert data into the table will it check them individually or as a
> composite?
>
> for example if i inserted the values
> col1 | col2
> 1, A
> 1, B
> 2, B
> 2, A
>
> if the above unique constraint is declared will it give me errors when
> inserting?
No. A good way of finding out is trying :-)
mysql> create table test (col1 int not null, col2 char(1) not null, unique
(col1, col2));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into test values (1, 'A');
Query OK, 1 row affected (0.00 sec)
mysql> insert into test values (1, 'B');
Query OK, 1 row affected (0.00 sec)
mysql> insert into test values (2, 'B');
Query OK, 1 row affected (0.00 sec)
mysql> insert into test values (2, 'A');
Query OK, 1 row affected (0.00 sec)
mysql> insert into test values (2, 'A');
ERROR 1062: Duplicate entry '2-A' for key 1
> neither col1 or col2 are a primary key but together they could be
> considered a composite candidate key pair
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