如何使用mysql将查询结果存储在变量中

Question

SET @v1 := SELECT COUNT(*) FROM user_rating;
SELECT @v1

当我使用

set

变量执行此查询时，会显示此错误。

Error Code : 1064
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use
near 'SELECT count(*) FROM user_rating' at line 1

Execution Time : 00:00:00:000
Transfer Time  : 00:00:00:000
Total Time     : 00:00:00:000

(1 row(s) returned)
Execution Time : 00:00:00:343
Transfer Time  : 00:00:00:000
Total Time     : 00:00:00:343

Answer 1

用括号括住该选择。

SET @v1 := (SELECT COUNT(*) FROM user_rating);
SELECT @v1;

Answer 2

此外，如果您想通过一个查询一次设置多个变量，您可以使用另一种语法来设置变量，如下所示：

SELECT @varname:=value

。

一个实际例子：

SELECT @total_count:=COUNT(*), @total_price:=SUM(quantity*price) FROM items ...

Answer 3

用这个

 SELECT weight INTO @x FROM p_status where tcount='value' LIMIT 1;

经过测试，工作正常...

Answer 4

Select count(*) from table_name into @var1; 
Select @var1;

Answer 5

如果您想将查询结果保存为临时表以便在后续查询中重用，请使用 MySQL

CREATE TEMPORARY TABLE

。

参见：https://dev.mysql.com/doc/refman/8.0/en/create-temporary-table.html

DROP TEMPORARY TABLE IF EXISTS myDb.temp_variable; -- drop just in case
CREATE TEMPORARY TABLE myDb.temp_variable SELECT * FROM myDb.student ORDER BY id DESC LIMIT 25;
SELECT * FROM myDb.temp_variable;

DROP TEMPORARY TABLE IF EXISTS myDb.temp_variable; -- drop after executing out scripts