MySQL 8.4 Release Notes
5.6.5 使用用户定义的变量
You can employ MySQL user variables to remember results without having to store them in temporary variables in the client. (See Section 11.4, “User-Defined Variables”.)
For example, to find the articles with the highest and lowest price you can do this:
mysql> SELECT @min_price:=MIN(price),@max_price:=MAX(price) FROM shop;
mysql> SELECT * FROM shop WHERE price=@min_price OR price=@max_price;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
Note
It is also possible to store the name of a database object such as a table or a column in a user variable and then to use this variable in an SQL statement; however, this requires the use of a prepared statement. See Section 15.5, “Prepared Statements”, for more information.