[SQL] Non Matching Records in Two Tables

[Ken Hill]

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