Tips for using coalesce () in mysql

Tips for using coalesce () in mysql

Coalesce () Explanation

The first non-empty expression in the return parameter (from left to right, and so on); Tips for using coalesce () in mysql

Example

A, B, and c variables.

Select coalesce (null, 2, 3); // Return 2

Select coalesce (null, null, 3); // Return 3

Select coalesce (1, 2, 3); // Return 1

As shown in the preceding example, the function is to return the first non-null value of the input parameter.

Select coalesce (NULL, NULL, 1 );

-- Return 1

If all input parameters are null, null is returned, for example

Select coalesce (NULL, NULL );

-- Return NULL

This parameter is used in the following scenarios: If a field is null by default, you can use this function instead of null, but for example, 0 or other values.

Select coalesce (field name, 0) as value from t; // (if the default value of the database Commission field is not 0, it must be developed.