Solved

how does mysql handle NULLs in indexes

Posted on 2014-01-10
2
402 Views
Last Modified: 2014-01-10
Hello

I'm a little unsure about how mysql handles nulls in indexes.

Can I have an index on a column that contains Nulls?

If I have an index based on a text field which can contain Nulls will mysql add the nulls to the index? Will they be added at the top or bottom if they are added (not that that matters 0 I'm just curious).

thanks
0
Comment
Question by:andieje
2 Comments
 
LVL 59

Accepted Solution

by:
Kevin Cross earned 250 total points
ID: 39771114
Hi.

Yes, you can have an index on a column that contains NULLs.  According to the manual, MySQL can leverage an index on column with NULLs to optimize IS NULL condition in WHERE clause.  Therefore, the answer is yes to your questions.

MySQL orders NULLs first if I remember correctly.
0
 
LVL 143

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 250 total points
ID: 39771156
from what I know, NULL values are NOT indexed.

however, indeed some optimizations are done for NULL values vs NOT NULL query:
http://dev.mysql.com/doc/refman/5.0/en/is-null-optimization.html
0

Featured Post

NFR key for Veeam Backup for Microsoft Office 365

Veeam is happy to provide a free NFR license (for 1 year, up to 10 users). This license allows for the non‑production use of Veeam Backup for Microsoft Office 365 in your home lab without any feature limitations.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

More Fun with XML and MySQL – Parsing Delimited String with a Single SQL Statement Are you ready for another of my SQL tidbits?  Hopefully so, as in this adventure, I will be covering a topic that comes up a lot which is parsing a comma (or other…
Password hashing is better than message digests or encryption, and you should be using it instead of message digests or encryption.  Find out why and how in this article, which supplements the original article on PHP Client Registration, Login, Logo…
A short tutorial showing how to set up an email signature in Outlook on the Web (previously known as OWA). For free email signatures designs, visit https://www.mail-signatures.com/articles/signature-templates/?sts=6651 If you want to manage em…
I've attached the XLSM Excel spreadsheet I used in the video and also text files containing the macros used below. https://filedb.experts-exchange.com/incoming/2017/03_w12/1151775/Permutations.txt https://filedb.experts-exchange.com/incoming/201…

840 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question