only non-existing rows

[nasht]

Hi,

I have 2 tables: tableFrom , tableTo.

I want to have the list of users that ARE in tableFrom, but NOT in tableTo.
The common field is "username".

I want all the rows from tableFrom as long as they don't already exist in tableTo.

An important point is that we use MySQL 4.0.20, so I can't use "NOT EXISTS(...)".

This query needs to be pretty fast since it might be ran many times an hour, even minutes.

Any ideas on how to write that?

Thank You,

Nathan

[sfullman]

<I want to have the list of users that ARE in tableFrom, but NOT in tableTo.
The common field is "username".>

to find:
SELECT
tableFrom.username
FROM
tableFrom LEFT JOIN tableTo ON tableFrom.username=tableTo.username
WHERE tableTo.username IS NULL

to insert these values over (if you want to do that):
INSERT INTO tableTo(
field list, ..
)
SELECT
tableFrom.username, ... etc...
FROM
tableFrom LEFT JOIN tableTo ON tableFrom.username=tableTo.username
WHERE tableTo.username IS NULL