mos wrote:
I have a merge table that is a union of 20 1 million row tables. Select
rows from it is quite fast. However if I want to delete all the rows as in:
delete from MyMergeTable;
it takes just over 3 minutes. I could execute 20 separate delete
statements for each of the 20 tables and it would complete in under a
second. Why is a Delete on a merge table so inefficient? It appears it
is deleting all the rows individually.
That's the way delete works - it deletes the rows one at a time. It also
has to update the indexes as it goes to remove links between the data &
index.
http://dev.mysql.com/doc/refman/5.0/en/delete.html
http://dev.mysql.com/doc/refman/5.0/en/delete-speed.html
If you're clearing the whole table, use truncate as Jerry suggested.
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