Shulou(Shulou.com)06/01 Report--

SQL has the ISNULL method, which is described as follows:

ISNULL

Replace NULL with the specified replacement value.

syntax

ISNULL ( check_expression , replacement_value )

parameters

check_expression

An expression that will be checked for NULL. check_expression can be any type.

replacement_value

The expression that will be returned if check_expression is NULL. replacement_value must be of the same type as check_expression.

For example:

SELECT count(ISNULL(age,0)) FROM Product;

However, in mysql, isnull is only used to determine whether it is empty, and it cannot implement the replacement function.(Incorrect parameter count in the call to native function 'isnull' Errornumber:1582).

So how does MySQL implement ISNULL in SQL?

IFNULL( check_expression , replacement_value ) implements the ISNULL method in SQL.

Again, the example above:

SELECT count(IFNULL(Weight, 50)) FROM Product;

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