SQL NULLIF function is not well known but could be very useful in some cases. It takes 2 parameters: it returns NULL if the 2 parameters are equal, otherwise it returns the value of the first parameter.
SQL NULLIF Function Syntax
NULLIF(expression1, expression2)
SQL NULLIF Function Example
Table: Users
| UserId | userName | screenName |
|---|---|---|
| 1 | Liysheet | Liy Sheet |
| 2 | Mohisy | Mohisy |
| 3 | Nuoo | Nuhoo |
| 4 | Mhquu | Mhquu |
| 5 | Yuhiaa | Uhiooo |
Show NULL if userName is equal to screenName, otherwise show userName:
SELECT userId, NULLIF(userName, screenName) FROM Users
The result will look like:
| UserId | NULLIF(userName, screenName) |
|---|---|
| 1 | Liysheet |
| 2 | NULL |
| 3 | Nuoo |
| 4 | NULL |
| 5 | Yuhiaa |