Tuesday, 17 July 2018

MySQL Sort Order with NULL

MySQL Sort Order with NULL

As a MySQL programmer, I often need to sort lists in alphabetical or numeric order, but many times the columns I use have null values. When ORDER BY col ASC is used, null vales appear at the top of the list; with DESC they appear at the bottom. Often, I would like a list to sort in alphabetical or numeric order, but with NULL at the bottom. Example: You have a table that stores user information, including nicknames. You users can search this table so that they can find friends on your site. When the sort by nickname, you would like for people without nicknames to be on the bottom of the list. Try: SELECT * FROM people ORDER BY nickname ASC Doesn't work, does it? It returns something like:

nicknamename
NULLArt
NULLMary
AbbyAbigal
BobbyRobert
CindyCynthia

All the NULL values are on top. What to do? Try this: SELECT * , nickname IS NULL AS isnull FROM people ORDER BY isnull ASC, nickname ASC

nicknamenameisnull
AbbyAbigal0
BobbyRobert0
CindyCynthia0
NULLArt1
NULLMary1

What's Happening?

[nickname IS NULL AS isnull] adds a column named "isnull" and fills it with a 0 if there is a value for nickname, and 1 if nickname is NULL. We sort first on this "isnull" column, which puts nicknames first, and null values last. We then sort alphabetically by nickname.

You can also shorten this up by using the ISNULL() function. The ISNULL() function returns 1 if the parameter is null, and 0 otherwise. The query now looks like: SELECT * FROM people ORDER BY ISNULL(nickname), nickname ASC; It will return:

nicknamename
AbbyAbigal
BobbyRobert
CindyCynthia
NULLArt
NULLMary

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