On Sat, 1999-09-04 16:37:20 +0800, Mark Hendley wrote:
> The releveant parts of the two tables are:
> Table User: USID (User ID that is Primary Key)
> Table UDetails: UDID (Primary Key) and USID (connection to User)
> Now for each entry in UDetails there 'should' be a corresponding
> entry in User. UDetails table stores a users Details and User stores
> his/her username and the MD5 hash of their username+password (USID).
> However, doing a count(*) for each table I find UDetails has 940 and
> User has 948 ! :)
> Is there a way to join the tables and show what is NOT common to
> both with regard to the USID field.
> I'm sure the answer is fairly easy :) but too many hours coding and
> flu are interfering with normal rational thought on this end.
The trick is to use a LEFT JOIN and test for the rows, where no
matching row of the second table has been found:
FROM UDetails LEFT JOIN User ON UDetails.USID=User.USID
WHERE User.USID IS NULL;
Try this query to see what happens internally:
FROM UDetails LEFT JOIN User ON UDetails.USID=User.USID;
Happy weekend wishes,
Martin Ramsch <m.ramsch@stripped> <URL: http://home.pages.de/~ramsch/ >
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