计算 MySQL 中的常见元素？
要计算常见元素，请使用COUNT()和GROUPBY。让我们首先创建一个表-
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Number int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable(Number) values(10); mysql> insert into DemoTable(Number) values(20); mysql> insert into DemoTable(Number) values(20); mysql> insert into DemoTable(Number) values(30); mysql> insert into DemoTable(Number) values(10); mysql> insert into DemoTable(Number) values(10);
使用select语句显示表中的所有记录-
mysql> select *from DemoTable;
这将产生以下输出-
+----+--------+ | Id | Number | +----+--------+ | 1 | 10 | | 2 | 20 | | 3 | 20 | | 4 | 30 | | 5 | 10 | | 6 | 10 | +----+--------+ 6 rows in set (0.00 sec)
以下是计算常见元素的查询-
mysql> select Number,count(Number) as CommonElement from DemoTable group by Number;
这将产生以下输出-
+--------+---------------+ | Number | CommonElement | +--------+---------------+ | 10 | 3 | | 20 | 2 | | 30 | 1 | +--------+---------------+ 3 rows in set (0.00 sec)