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WHERE Condition limit, in PHP call to MySQL DB

     
12:49 am on Apr 5, 2011 (gmt 0)

5+ Year Member



Hi, I am dealing with some MySQL tables with large amounts of columns. I am wondering is there a limit to the number of conditions a MySQL SELECT statement can handle?

i.e. SELECT * FROM table WHERE something = "1" AND somethingelse = "2" AND ... AND ... AND ...;

Is there a way to optimise this, knowing that the table could have 150 columns?
5:53 am on Apr 5, 2011 (gmt 0)

WebmasterWorld Senior Member 5+ Year Member



Hi there Username,

I have no idea, and never really thought about that - personally I would post this in the databases section, as there are people in there who may answer this or show a way of optimising this for you.

I have seen queries get quite large though, so possibly this is a natural thing for mysql to handle.

Sorry I can't be more helpful.

Cheers,
MRb
10:41 pm on Apr 5, 2011 (gmt 0)

5+ Year Member



So, does anyone else have any ideas on this?
12:16 am on Apr 6, 2011 (gmt 0)

WebmasterWorld Senior Member demaestro is a WebmasterWorld Top Contributor of All Time 10+ Year Member



I have never come across one
12:22 am on Apr 6, 2011 (gmt 0)

WebmasterWorld Senior Member eelixduppy is a WebmasterWorld Top Contributor of All Time 5+ Year Member



All I could find....


A communication packet is a single SQL statement sent to the MySQL server, a single row that is sent to the client, or a binary log event sent from a master replication server to a slave.

The largest possible packet that can be transmitted to or from a MySQL 5.0 server or client is 1GB.


[dev.mysql.com...]
5:37 am on Apr 6, 2011 (gmt 0)

WebmasterWorld Senior Member 5+ Year Member



>>The largest possible packet that can be transmitted to or from a MySQL 5.0 server or client is 1GB

Well I shan't worry about sql queries being over 100 or so lines again!

Nice find EelixDuppy, and thanks for sharing.

Cheers,
MRb
4:32 pm on Apr 6, 2011 (gmt 0)

WebmasterWorld Senior Member rocknbil is a WebmasterWorld Top Contributor of All Time 10+ Year Member



Like most things mySQL, limitations are more likely to be hardware, OS, and memory dependent than any set limits.

If you have tables 150 columns wide, and that many "and's" or "or's" in your selects, it may be a good time to re-think your database structure and split it up into multiple tables. Look into database normalization.
 

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