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

用括号选择的环绕声。

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，则可以使用其他语法设置如下所示的变量：SELECT @varname:=value。

一个实际的例子：

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

Answer 3

使用此

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

测试并且工作得很好......

Answer 4

我正在尝试在这里做类似的事情。但是，我的 SQL 语法出现错误：

SET @dc = (SELECT CONCAT('DROP SCHEMA IF EXISTS ', SCHEMA_NAME,';') FROM information_schema.SCHEMATA WHERE SCHEMA_NAME = 'tc1-student');
SELECT @dc;
PREPARE drop_dc FROM @dc;
EXECUTE drop_dc;
DEALLOCATE PREPARE drop_dc;

实际的 SELECT 查询确实正常工作。但是当设置尝试从@dc 变量准备语句时，我收到一个 SQL 语法错误。这里有什么突出的吗？

Answer 5

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