Questions And Answers

More Tutorials

MYSQL Performance Tuning

Don't hide in function

A common mistake is to hide an indexed column inside a function call. For example, this can't be helped by an index:

WHERE DATE(dt) = '2000-01-01'

Instead, given INDEX(dt) then these may use the index:

WHERE dt = '2000-01-01' -- if `dt` is datatype `DATE`

This works for DATE, DATETIME, TIMESTAMP, and even DATETIME(6) (microseconds):

WHERE dt >= '2000-01-01'
 AND dt < '2000-01-01' + INTERVAL 1 DAY


In general OR kills optimization.

WHERE a = 12 OR b = 78

cannot use INDEX(a,b), and may or may not use INDEX(a), INDEX(b) via "index merge". Index merge is better than nothing, but only barely.

WHERE x = 3 OR x = 5

is turned into

WHERE x IN (3, 5)

which may use an index with x in it.

Add the correct index

This is a huge topic, but it is also the most important "performance" issue.

The main lesson for a novice is to learn of "composite" indexes. Here's a quick example:

INDEX(last_name, first_name)

is excellent for these:

WHERE last_name = '...'
WHERE first_name = '...' AND last_name = '...' -- (order in WHERE does not matter)

but not for

WHERE first_name = '...' -- order in INDEX _does_ matter
WHERE last_name = '...' OR first_name = '...' -- "OR" is a killer


In this page (written and validated by ) you learned about MYSQL Performance Tuning . What's Next? If you are interested in completing MYSQL tutorial, your next topic will be learning about: MYSQL Have an INDEX.

Incorrect info or code snippet? We take very seriously the accuracy of the information provided on our website. We also make sure to test all snippets and examples provided for each section. If you find any incorrect information, please send us an email about the issue:

Share On:

Mockstacks was launched to help beginners learn programming languages; the site is optimized with no Ads as, Ads might slow down the performance. We also don't track any personal information; we also don't collect any kind of data unless the user provided us a corrected information. Almost all examples have been tested. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. By using, you agree to have read and accepted our terms of use, cookies and privacy policy.