Comments on: UNION vs UNION ALL Performance http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/ Everything about MySQL Performance Tue, 02 Dec 2008 17:28:54 +0000 http://wordpress.org/?v=2.5.1 By: techfounder » Optimizing OR (union) operations in MySQL http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-362007 techfounder » Optimizing OR (union) operations in MySQL Wed, 15 Oct 2008 06:29:09 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-362007 [...] our OR condition with two UNION’ed select statements (the inspiration is from a couple of posts over at the MySQL performance blog). Breaking the original query into a UNION form results [...] [...] our OR condition with two UNION’ed select statements (the inspiration is from a couple of posts over at the MySQL performance blog). Breaking the original query into a UNION form results [...]

]]> By: Charu http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-300973 Charu Mon, 19 May 2008 06:55:23 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-300973 Hi, Can someone answer my related query posted in the mysql performance forum.Query can be found here: http://forum.mysqlperformanceblog.com/s/mv/tree/743/ Thanks. Hi,

Can someone answer my related query posted in the mysql performance forum.Query can be found here:

http://forum.mysqlperformanceblog.com/s/mv/tree/743/

Thanks.

]]> By: Sebastian Gomez Morales http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-257267 Sebastian Gomez Morales Tue, 25 Mar 2008 22:45:58 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-257267 great article! (as usual) thanks a lot. i was looking for this and this text was very helpful keep the good work, boys great article! (as usual)
thanks a lot.
i was looking for this and this text was very helpful
keep the good work, boys

]]> By: ramasubramanian.G http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-255074 ramasubramanian.G Fri, 21 Mar 2008 09:45:14 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-255074 sldfj sldfj

]]> By: [PHP/MYSQL] Datenbankabfrage - Forum Fachinformatiker.de http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-212960 [PHP/MYSQL] Datenbankabfrage - Forum Fachinformatiker.de Wed, 05 Dec 2007 23:56:01 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-212960 [...] Warum? UNION vs UNION ALL Performance | MySQL Performance Blog __________________ Siste gradum teque aspectu ne subtrahe nostro! Quem fugis? Extremum fato, quod [...] [...] Warum? UNION vs UNION ALL Performance | MySQL Performance Blog __________________ Siste gradum teque aspectu ne subtrahe nostro! Quem fugis? Extremum fato, quod [...]

]]> By: peter http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-186775 peter Thu, 08 Nov 2007 21:06:08 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-186775 Hey Scott, This is what I mentioned too. The point was not to see if it is faster but to get the measure of the thing in numbers. Hey Scott,

This is what I mentioned too. The point was not to see if it is faster but to get the measure of the thing in numbers.

]]> By: Scott Marlowe http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-186685 Scott Marlowe Thu, 08 Nov 2007 17:48:35 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-186685 Union All is generally faster than union because it doesn't have to do a sort / unique step. With union all, you smoosh two data sets together not caring if there are dups or not. union (distinct) has to then go that extra step to remove dups. TANSTAAFL Union All is generally faster than union because it doesn’t have to do a sort / unique step.

With union all, you smoosh two data sets together not caring if there are dups or not. union (distinct) has to then go that extra step to remove dups.

TANSTAAFL

]]> By: Pythian Group Blog » Blog Archive » Log Buffer #66: a Carnival of the Vanities for DBAs http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-176801 Pythian Group Blog » Blog Archive » Log Buffer #66: a Carnival of the Vanities for DBAs Fri, 12 Oct 2007 16:34:05 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-176801 [...] Peter Zaitsev of the MySQL Performance Blog compares the performance of UNION vs. UNION ALL. [...] [...] Peter Zaitsev of the MySQL Performance Blog compares the performance of UNION vs. UNION ALL. [...]

]]> By: peter http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-175272 peter Sat, 06 Oct 2007 09:01:40 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-175272 Baron, I think the most important thing here is the fact even UNION ALL uses temporary table, while it could simply be sending result sets one after another in many cases, possibly with little conversion to adjust data types. The unique index is in fact not index on all columns but some form of hash index - with MyISAM key limit index on all columns would not work for tables with long rows not to mention BLOBs Baron,

I think the most important thing here is the fact even UNION ALL uses temporary table, while it could simply be sending result sets one after another in many cases, possibly with little conversion to adjust data types.

The unique index is in fact not index on all columns but some form of hash index - with MyISAM key limit index on all columns would not work for tables with long rows not to mention BLOBs

]]> By: Xaprb http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-175166 Xaprb Sat, 06 Oct 2007 01:07:52 +0000 http://www.mysqlperformanceblog.com/2007/10/05/union-vs-union-all-performance/#comment-175166 I read the source for UNION once (Mark Leith pointed me to it). It's not very much code. The only difference between the two is the temporary table has the "distinct" property set, as I recall. So of course that means a unique index on all columns, which is bound to be slow. We should mention this in our book... it's such an instinct for me to use UNION ALL that I forgot about it. I'll go look and see if we have mentioned it anywhere. I read the source for UNION once (Mark Leith pointed me to it). It’s not very much code. The only difference between the two is the temporary table has the “distinct” property set, as I recall. So of course that means a unique index on all columns, which is bound to be slow.

We should mention this in our book… it’s such an instinct for me to use UNION ALL that I forgot about it. I’ll go look and see if we have mentioned it anywhere.

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