Help!
Probably it is too easy, but I am not so experienced in MySQL up to now.
I have two tables table1&table2 with the following columns: col1 double,
col2 int(11), col3 date
I want to query:
INSERT INTO table2 SELECT col1,col2,col3 FROM table1
WHERE col2= ( SELECT MAX(col2)
FROM table1
WHERE table1.col1=table2.col1 AND
table1.col3=table2.col3
);
It is working fine, but not very fast. Do you know the best solution,
probably a multi-column index (INDEX indexname(col1,col3))? Or do I need
an index also for col2?
Thanks,
Matthias
8  4923 
On Sun, 30 Nov 2003 02:14:47 +0100, Matthias Braun <ma*******@web.de>
wrote: It is working fine, but not very fast. Do you know the best solution,
probably a multi-column index (INDEX indexname(col1,col3))? Or do I need
an index also for col2?
Mysql can only use one index per table. So, a multi-column index
would be the right way to go.
If you built your index with Col1,Col3, then any "where" with Col1 and
Col3 can be optimized with that index. And any "where" with just
col1 can be optimized, but a "where" with just col3 would NOT be able
to use the index.
Chuck Gadd http://www.csd.net/~cgadd/aqua
On Sun, 30 Nov 2003 02:14:47 +0100, Matthias Braun <ma*******@web.de>
wrote: It is working fine, but not very fast. Do you know the best solution,
probably a multi-column index (INDEX indexname(col1,col3))? Or do I need
an index also for col2?
Mysql can only use one index per table. So, a multi-column index
would be the right way to go.
If you built your index with Col1,Col3, then any "where" with Col1 and
Col3 can be optimized with that index. And any "where" with just
col1 can be optimized, but a "where" with just col3 would NOT be able
to use the index.
Chuck Gadd http://www.csd.net/~cgadd/aqua
On Sat, 29 Nov 2003 18:21:27 -0700, I wrote: Mysql can only use one index per table.
Mysql can only use one index per table PER QUERY.
Chuck Gadd http://www.csd.net/~cgadd/aqua
On Sat, 29 Nov 2003 18:21:27 -0700, I wrote: Mysql can only use one index per table.
Mysql can only use one index per table PER QUERY.
Chuck Gadd http://www.csd.net/~cgadd/aqua
On Sun, 30 Nov 2003 02:51:07 +0100, Matthias Braun <ma*******@web.de>
wrote:
I am using MySQL 4.1.0-alpha. Only one index is used for that query,
but the index is a multi-column index, see also
I know about multi-colum indexes. I was basically just saying that
you need to use a multi-column index. You could not just create three
seperate single-field indexes and have mysql use them all on the same
query.
But I did mis-read your original posted query.
Lets see, it does:
select ... from table1 where col2=x
So you would need an index on table1.col2 by itself.
And it does
select max(col2) from table1 where table1.col1=table2.col1
and table1.col3=table2.col3
So you'd need an index on table1.col1+table1.col3 and
table2.col1+table2.col3
I am GUESSING that mysql would be able to use two different
indexes, since they really are seperate queries. I haven't played
with sub-selects much in mysql, so I'm not sure what the optimizer
will do. And in fact, the optimizer might not do a great job yet.
Chuck Gadd http://www.csd.net/~cgadd/aqua
On Sun, 30 Nov 2003 02:51:07 +0100, Matthias Braun <ma*******@web.de>
wrote:
I am using MySQL 4.1.0-alpha. Only one index is used for that query,
but the index is a multi-column index, see also
I know about multi-colum indexes. I was basically just saying that
you need to use a multi-column index. You could not just create three
seperate single-field indexes and have mysql use them all on the same
query.
But I did mis-read your original posted query.
Lets see, it does:
select ... from table1 where col2=x
So you would need an index on table1.col2 by itself.
And it does
select max(col2) from table1 where table1.col1=table2.col1
and table1.col3=table2.col3
So you'd need an index on table1.col1+table1.col3 and
table2.col1+table2.col3
I am GUESSING that mysql would be able to use two different
indexes, since they really are seperate queries. I haven't played
with sub-selects much in mysql, so I'm not sure what the optimizer
will do. And in fact, the optimizer might not do a great job yet.
Chuck Gadd http://www.csd.net/~cgadd/aqua This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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