How does the isnull function in MSSQL be implemented in MySQL...

How to Implement the isnull function in mssql in mysql

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IFNULL (expr1, expr2)
If expr1 is not NULL, the returned value of IFNULL () is expr1;
Otherwise, the returned value is expr2. The returned value of IFNULL () is a number or string, depending on the context in which it is used.

Code

Mysql> select ifnull (1, 0 );

-> 1

Mysql> select ifnull (NULL, 10 );


-> 10

Mysql> select ifnull (1/0, 10 );

-> 10

Mysql> select ifnull (1/0, 'yes ');

-> 'Yes'

 

The default result value of ifnull (expr1, expr2) is one of the two expressions that is more "common", in the order of string, real, or
Integer. Assume that an expression-based table or MySQL must store the returned value of ifnull () in a temporary table in internal memory:

 

Create table tmp select ifnull (1, 'test') AS test;

 

In this example, the test column type is Char (4 ).

NULLIF (expr1, expr2)
If expr1 = expr2 is true, the return value is NULL. Otherwise, the return value is expr1. This is the same as case when expr1 = expr2 then null else expr1 END.

Mysql> select nullif (1, 1 );

-> NULL

Mysql> select nullif (1, 2 );

-> 1

 

Note: If the parameters are not equal, the value obtained by MySQL twice is expr1.