计算 MySQL 表中记录的出现次数并在新列中显示结果?
mysqlmysqli database更新于 2024/1/1 4:30:00
为此，请使用 COUNT(*) 和 GROUP BY 子句。让我们首先创建一个表 −
mysql> create table DemoTable1942 ( Value 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 DemoTable1942 values(1); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1942 values(2); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1942 values(3); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1942 values(2); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1942 values(3); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1942 values(3); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1942 values(1); 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 DemoTable1942;
这将产生以下输出 −
+-------+ | Value | +-------+ | 1 | | 2 | | 3 | | 2 | | 3 | | 3 | | 1 | +-------+ 7 rows in set (0.00 sec)
这是计算出现次数的查询:
mysql> select Value, count(*) from DemoTable1942 group by Value;
这将产生以下输出 −
+-------+----------+ | Value | count(*) | +-------+----------+ | 1 | 2 | | 2 | 2 | | 3 | 3 | +-------+----------+ 3 rows in set (0.00 sec)
