Question

I’d like to select all records from a table (names) where lastname is not unique. Preferably I would like to delete all records that are duplicates.

How would this be done? Assume that I don’t want to rerun one query multiple times until it quits.

Answer 1

The fastest and easiest way to delete duplicate records is my issuing a very simple command.

ALTER IGNORE TABLE [TABLENAME] ADD UNIQUE INDEX UNIQUE_INDEX ([FIELDNAME])

This will lock the table, if this is an issue, try:

delete t1 from table1 t1, table2 t2
where table1.duplicate_field= table2.duplicate_field (add more if need ie. and table.duplicate_field2=table2.duplicate_field2)
and table1.unique_field > table2.unique_field
and breakup into ranges to run faster