Ken Hill wrote:
> I need some help with a bit of SQL. I have two tables. I want to find
> records in one table that don't match records in another table based
> on a common column in the two tables. Both tables have a column named
> 'key100'. I was trying something like:
>
> SELECT count(*)
> FROM table1, table2
> WHERE (table1.key100 != table2.key100);
>
> But the query is very slow and I finally just cancel it. Any help is
> very much appreciated.
>
> -Ken
Maybe you could use a NOT EXISTS subquery, as in
SELECT count(*) from table1
WHERE NOT EXISTS(SELECT count(*) from table2 WHERE table1.key100
=table2.key100)
which gives you the number of records in table1 without corresponding
records in table2.
That kind of query is quite fast, if there exists an index on table2.key100
hth
P.Jacquot
