Union does a distinct on all results.  UNION ALL will avoid that.

Regards,
Gavin Towey

-----Original Message-----
From: chen.1...@gmail.com [mailto:chen.1...@gmail.com] On Behalf Of chen jia
Sent: Monday, April 05, 2010 11:07 AM
To: mysql@lists.mysql.com
Subject: Slow Union Statement

Hi there,

I run simple statement like this:

create table c
select * from a
union
select * from b;

where table a has 90,402,534 rows, and table b has 33,358,725 rows.
Both tables have the same three variables.

It's taken a long time, more than half an hour now. How do I make it faster?

Best,
Jia

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