计算重复的ID，并在MySQL的单独列中显示结果
让我们首先创建一个表-
mysql> create table DemoTable1453 -> ( -> CustomerId int, -> CustomerReviewNumber int -> );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1453 values(10,4); mysql> insert into DemoTable1453 values(10,4); mysql> insert into DemoTable1453 values(11,5); mysql> insert into DemoTable1453 values(11,5); mysql> insert into DemoTable1453 values(11,5); mysql> insert into DemoTable1453 values(13,2); mysql> insert into DemoTable1453 values(11,5); mysql> insert into DemoTable1453 values(10,4); mysql> insert into DemoTable1453 values(13,2);
使用select语句显示表中的所有记录-
mysql> select * from DemoTable1453;
这将产生以下输出-
+------------+----------------------+ | CustomerId | CustomerReviewNumber | +------------+----------------------+ | 10 | 4 | | 10 | 4 | | 11 | 5 | | 11 | 5 | | 11 | 5 | | 13 | 2 | | 11 | 5 | | 10 | 4 | | 13 | 2 | +------------+----------------------+ 9 rows in set (0.00 sec)
以下是计算重复ID的查询-
mysql> select CustomerId,count(distinct CustomerReviewNumber) -> from DemoTable1453 -> group by CustomerId;
这将产生以下输出-
+------------+--------------------------------------+ | CustomerId | count(distinct CustomerReviewNumber) | +------------+--------------------------------------+ | 10 | 1 | | 11 | 1 | | 13 | 1 | +------------+--------------------------------------+ 3 rows in set (0.14 sec)