计算MySQL表中记录的出现次数，并将结果显示在新列中？
为此，将COUNT（*）与GROUPBY子句一起使用。让我们首先创建一个表-
mysql> create table DemoTable1942 ( Value int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1942 values(1); mysql> insert into DemoTable1942 values(2); mysql> insert into DemoTable1942 values(3); mysql> insert into DemoTable1942 values(2); mysql> insert into DemoTable1942 values(3); mysql> insert into DemoTable1942 values(3); mysql> insert into DemoTable1942 values(1);
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)
这是查询发生次数的查询：
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)