MySQL IsNull () and ifnull () are null and are NOT NULL

Usergrade table

1. Find the line where username is null

SELECT * from Usergrade WHERE ISNULL (USERNAME)

SELECT * from Usergrade WHERE USERNAME is NULL

2. Find the line inside username NOT NULL

SELECT * from Usergrade WHERE USERNAME are not NULL

3. List all rows, and replace the field with username null with LXY

SELECT ifnull (USERNAME, ' lxy '), GRADE from Usergrade

IF (' Apformid ' is null,0,1) Hasplan

If Apformid is null, choose 0, not select 1

MySQL IsNull () and ifnull () are null and are NOT NULL