The SQL ISNULL function has different meanings in different databases. In MS SQL Server, ISNULL is used to replace NULL value, while in MySQL, ISNULL is used to tell if an expression is NULL or not.
SQL Server
In SQL Server, the SQL ISNULL function is used to replace NULL value with an alternate value. It’s same with the SQL NVL function in Oracle or SQL IFNULL function in mySQL.
SQL ISNULL Function in MS SQL Server Syntax
ISNULL(exp1, exp2)
If exp1 is null, the ISNULL function will return exp2, otherwise it will return exp1.
SQL ISNULL Function in MS SQL Server Example
Table: Employees
| ID | EmpName |
|---|---|
| 001 | Juiaaa |
| 002 | Hiooi |
| 003 | NULL |
| 004 | Qiak |
SELECT ID, ISNULL(EmpName, 'N/A') AS EmpName FROM Employees
The result will look like:
| ID | EmpName |
|---|---|
| 001 | Juiaaa |
| 002 | Hiooi |
| 003 | N/A |
| 004 | Qiak |
MySQL
In MySQL, the SQL ISNULL function is used to tell if an expression is NULL or not.
SQL ISNULL Function in MySQL Syntax
ISNULL(exp1)
If exp1 is null, the ISNULL function will return 1, otherwise it will return 0.
SQL ISNULL Function in MySQL Example
Table: Employees
| ID | EmpName |
|---|---|
| 001 | Juiaaa |
| 002 | Hiooi |
| 003 | NULL |
| 004 | Qiak |
SELECT ID, ISNULL(EmpName) AS NoName FROM Employees
The result will look like:
| ID | NoName |
|---|---|
| 001 | 0 |
| 002 | 0 |
| 003 | 1 |
| 004 | 0 |