How to use IFNULL, NULLIF and ISNULL in MySql

1. The expression of IFNULL is as follows:

IFNULL(expr1,expr2)

Function description: If expr1 is null, the function returns expr2, otherwise it will Return expr1.

Example 1:

SELECT IFNULL(0,'ab');

The first parameter is 0, not NULL, so the result is 0.

Example 2:

SELECT IFNULL(NULL,'ab');

The first parameter is NULL, so the result is ab.

2. The expression of NULLIF is as follows:

SELECT NULLIF(expr1,expr2)

Function description: If two If the two parameters are equal, NULL is returned; otherwise, the first parameter is returned.

Example 1:

SELECT NULLIF('a','b');

The two parameters are not equal, so the result is the first parameter a.

Example 2:

SELECT NULLIF('a','a');

The two parameters are equal, so the result is NULL.

3. The expression of ISNULL is as follows:

SELECT ISNULL(expr)

Function description: If expr is null, then isnull() The return value is 1, otherwise the return value is 0.

Example 1:

SELECT ISNULL(NULL);

The parameter is NULL, so the result is 1.

Example 2:

SELECT ISNULL('ab');

The parameter is not NULL, so the result is 0.

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