Moral of the story: Don't forget to check for duplicates, because My ISAM doesn't.
If IGNORE is provided, all errors encountered during the update are ignored.
The implicit default value is tables for which there are foreign key constraints, the My SQL optimizer might process tables in an order that differs from that of their parent/child relationship. Instead, update a single table and rely on the provides to cause the other tables to be modified accordingly. COLUMN2 IS NULLAn outerjoin is performed based on the equijoin condition.
See Section 15.8.7, “Inno DB and FOREIGN KEY Constraints”. Records not matching the equijoin from table2 are marked with null.
I was not able, using my SQL 4.1.1, to do this as a subquery: UPDATE Groups LEFT JOIN (SELECT Group Id, MIN(Val Within Group) AS base Val FROM Groups GROUP BY Group Id) AS Grp Sum USING (Group Id) SET Val Within Group=Val Within Group-base Val; Csaba Gabor UPDATE Syntax with "on-line" updating value limitations.