Re: Multiple Alter Table Statements in one batch

I've done some tests on this ...

and I get different results to you....

Using a table of 1,000,000 rows with no indexes and

     adding 2 columns at once took about 4s

     adding 2 columns with 2 commands took about 7s

So better to do it in one command

Using a table of 1,000,000 rows with a single index and

     adding 2 columns at once took about 9s

     adding 2 columns with 2 commands took about 15s (8s + 7s)

Still better as one command

(Note : lots of rounding in these )

If the data is flushed out of cache then the times increase by 50%.

Adding 2 columns with 2 commands took about 21s (14s + 8s)

The first alter table gets everything off disk and the second doesn't touch the disk so much faster.

I suspect you will see the same effect.

BTW, I also ran this on a 35m row table with 1 index and it took 9 minutes which is substantially faster than your run. What hardware are you using ? What disks are you using ?