Effects of order of columns, while defining an index on them, on the performance of the queries

Posted by Hossein on Stack Overflow See other posts from Stack Overflow or by Hossein
Published on 2010-05-13T22:21:30Z Indexed on 2010/05/13 22:24 UTC
Read the original article Hit count: 174

Filed under:

mysql

|

mysql-query

|

sql

|

query

|

indexing

Hi, Does order of the columns in an Index definition for a table in a database has any effect on the performance? for e.g. are these two queries different ? CREATE INDEX xxx ON tablex(col1,col2) CREATE INDEX xxx ON tablex(col2,col1)

what about the in case that I use a BTREE index? I am using Mysql. thanks

© Stack Overflow or respective owner

Related posts about mysql

How to remove MySQL completely with config and library files on ubuntu 12.04 gnome 3.0

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I tried everything till now: sudo apt-get remove mysql-server mysql-client mysql-common sudo apt-get purge mysql-server mysql-client mysql-common sudo apt-get autoremove and even more commands... But whenever I am trying to locate mysql. I get a no. of files related to mysql command: shell>>… >>> More
mysql: Cannot load from mysql.proc. The table is probably corrupted

as seen on Server Fault - Search for 'Server Fault'
Mysql was started: /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 but when I'm trying to do something: ERROR 1548 (HY000) at line 1: Cannot… >>> More
Why is there a /etc/init.d/mysql file on this Slackware machine? How could it have gotten there?

as seen on Server Fault - Search for 'Server Fault'
A client of my IT-consulting service owns a web-development shop. He's been having problems with a Slackware 12.0 server running MySQL 5.0.67. The machine was set up by the client's sysadmin, who left on bad terms. My client no longer employs a sysadmin. As far as I can tell, the only copy of MySQL… >>> More
mysql: Bind on unix socket: Permission denied

as seen on Server Fault - Search for 'Server Fault'
Can't start mysql with: sudo /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 120222 13:40:48 mysqld_safe Starting mysqld daemon with databases… >>> More
MySQL – Learning MySQL Online in 6 Hours – MySQL Fundamentals in 320 Minutes

as seen on SQL Authority - Search for 'SQL Authority'
MySQL is one of the most popular database language and I have been recently working with it a lot. Data have no barrier and every database have their own place. I have been working with MySQL for quite a while and just like SQL Server, I often find lots of people asking me if I have a tutorial which… >>> More

Related posts about mysql-query

MySQL query returns different set of results on two identical databases

as seen on Stack Overflow - Search for 'Stack Overflow'
I exported a live MySQL database (running mysql 5.0.45) to a local copy (running mysql 5.1.33) with no errors upon import. There is a view in the database, that when executed locally, returns a different set of data than when executed remotely. It's returning 32 results instead of 63. When I execute… >>> More
What's wrong with my MySql query ?!

as seen on Stack Overflow - Search for 'Stack Overflow'
This is a query I am doing with mysql using PHP This is the query line <?php $query = "SELECT * FROM node WHERE type = 'student_report' AND uid = '{$uid}' LIMIT 1 ORDER BY created DESC"; ?> I get the following error You have an error in your SQL syntax; check the manual that corresponds… >>> More
Optimizing the MySQL Query Cache

as seen on Internet.com - Search for 'Internet.com'
MySQL's query cache is an impressive piece of engineering if sometimes misunderstood. Keeping it optimized and used efficiently can make a big difference in the overall throughput of your application, so it's worth taking a look under the hood, understanding it, and then keeping it tuned optimally. >>> More
index help for a MySQL query using greater-than operator and ORDER BY

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a table with at least a couple million rows and a schema of all integers that looks roughly like this: start stop first_user_id second_user_id The rows get pulled using the following queries: SELECT * FROM tbl_name WHERE stop >= M AND first_user_id=N AND second_user_id=N… >>> More
mysql query using jdbc

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi all, I have the following table: Service_ID feedback 31 1 32 1 33 1 1 I have the sample code to find the sum: ResultSet res = st.executeQuery("SELECT Service_ID,SUM(consumer_feedback)… >>> More