Addyman的博客

Reference: https://dev.mysql.com/doc/refman/8.0/en/explain.html https://dev.mysql.com/doc/refman/8.0/en/explain-output.html 1、Obtaining Table Structure Information DESCRIBE|EXPLAIN order_tm_order...

COALESCE(value,...) Returns the first non-NULL value in the list, or NULL if there are no non-NULL values. 例子1：基础使用 mysql> SELECT COALESCE(NULL,1); -> 1 mysql> SELECT COALESCE(NUL...

UNION is used to combine the result from multiple SELECT statements into a single result set. The column names from the first SELECT statement are used as the column names for the results returned. S...