计数MySQL中多列的值？
要计算多列的值，请使用CASE语句。让我们首先创建一个表：：
mysql> create table countValueMultipleColumnsDemo -> ( -> Value1 int, -> Value2 int, -> Value3 int -> );
以下是使用insert命令在表中插入一些记录的查询：
mysql> insert into countValueMultipleColumnsDemo values(10,15,10); mysql> insert into countValueMultipleColumnsDemo values(20,30,10); mysql> insert into countValueMultipleColumnsDemo values(40,10,60);
以下是使用select命令显示表中记录的查询：
mysql> select *from countValueMultipleColumnsDemo;
这将产生以下输出
+--------+--------+--------+ | Value1 | Value2 | Value3 | +--------+--------+--------+ | 10 | 15 | 10 | | 20 | 30 | 10 | | 40 | 10 | 60 | +--------+--------+--------+ 3 rows in set (0.00 sec)
以下是对多个列的值进行计数的查询：
mysql> SELECT (SUM(CASE WHEN Value1 = 10 THEN 1 ELSE 0 END) + -> SUM(CASE WHEN Value2 = 10 THEN 1 ELSE 0 END) + -> SUM(CASE WHEN Value3 = 10 THEN 1 ELSE 0 END)) TOTAL_COUNT -> from countValueMultipleColumnsDemo;
这将产生以下输出
+-------------+ | TOTAL_COUNT | +-------------+ | 4 | +-------------+ 1 row in set (0.00 sec)