Summary of coalesce() usage tips in MySQL

Preface

Recently, I accidentally discovered MySQL's coalesce. I just had time, so I summarized the usage tips of coalesce() in MySQL and shared them with you. Let's take a look at the detailed introduction:

coalesce() explained

Returns the first non-empty expression in the argument (from left to right, and so on);

Usage Examples

There are three variables: a, b, and c.

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

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

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

As can be seen from the above example, its function is to return the first non-null value in the passed parameter.

SELECT COALESCE(NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, 1); 
-- Return 1

If all the passed parameters are null, null is returned, for example

SELECT COALESCE(NULL, NULL, NULL, NULL); 
-- Return NULL

This parameter is used when: if a field is null by default, and you want it to return something other than null, such as 0 or other values, you can use this function

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 developer's fault. Please don't criticize my personal opinion).

Summarize

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