Yes, that's the trick. Thank Rudy and Gavin.

Best,
Jia

On Mon, Apr 5, 2010 at 2:13 PM, Gavin Towey <gto...@ffn.com> wrote:
> 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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