MySQL查询从表的不同列中选择平均值？
为了获得平均值，AVG()请将其与DISTINCT结合使用，并根据不同的记录进行计算。让我们首先创建一个表-
mysql> create table DemoTable1934 ( StudentName varchar(20), StudentMarks int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1934 values('Chris',56);
mysql> insert into DemoTable1934 values('Chris',56);
mysql> insert into DemoTable1934 values('David',78);
mysql> insert into DemoTable1934 values('David',78);
mysql> insert into DemoTable1934 values('Carol',45);使用select语句显示表中的所有记录-
mysql> select * from DemoTable1934;
这将产生以下输出-
+-------------+--------------+ | StudentName | StudentMarks | +-------------+--------------+ | Chris | 56 | | Chris | 56 | | David | 78 | | David | 78 | | Carol | 45 | +-------------+--------------+ 5 rows in set (0.00 sec)
这是从表的不同列中选择平均值的查询-
mysql> select avg(tbl.StudentMarks) from ( select distinct StudentName,StudentMarks from DemoTable1934 ) as tbl;
这将产生以下输出-
+-----------------------+ | avg(tbl.StudentMarks) | +-----------------------+ | 59.6667 | +-----------------------+ 1 row in set (0.00 sec)