MySQL 查询从表的不同列中选择平均值?
mysqlmysqli database
要获取平均值，请使用 AVG() 并将其与 DISTINCT 结合使用，以从不同记录计算。让我们首先创建一个表 −
mysql> create table DemoTable1934 ( StudentName varchar(20), StudentMarks int ); Query OK, 0 rows affected (0.00 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1934 values('Chris',56);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('Chris',56);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('David',78);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('David',78);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1934 values('Carol',45);
Query OK, 1 row affected (0.00 sec)
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)
