Tips for using coalesce () in mysql, mysqlcoalesce

Tips for using coalesce () in mysql, mysqlcoalesce

Preface

Recently, I accidentally discovered mysql coalesce, and just happened to have timeCoalesce ()Below is a detailed introduction to the usage tips:

Coalesce () Explanation

Return the first non-null expression in the parameter (from left to right, and so on );

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 the development error. In my opinion, Do not spray it ).

Summary

The above is all the content of this article. I hope the content of this article will help you in your study or work. If you have any questions, please leave a message, thank you for your support.