极客教程是否可以结合’DISTINCT’和’COUNT’查询，以便我可以查看每个MySQL表列中出现的每个不同值的次数？
是的，您可以使用聚合函数COUNT(*)和GROUP BY子句。让我们首先创建一个-
mysql> create table DemoTable1425
-> (
-> 加入年份int
-> );
Query OK, 0 rows affected (0.76 sec)
使用插入在表中插入一些记录-
mysql> insert into DemoTable1425 values(2000);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable1425 values(2010);
Query OK, 1 row affected (0.24 sec)
mysql> insert into DemoTable1425 values(2015);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable1425 values(2000);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable1425 values(2010);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable1425 values(2000);
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1425 values(2010);
Query OK, 1 row affected (0.10 sec)
使用select显示来自表的所有记录-
mysql> select * from DemoTable1425;
这将生成以下输出-
+-------------+
| 加入年份 |
+-------------+
| 2000 |
| 2010 |
| 2015 |
| 2000 |
| 2010 |
| 2000 |
| 2010 |
+-------------+
7 rows in set (0.00 sec)
以下是查询每个不同值出现次数的查询-
mysql> select JoiningYear,count(*) from DemoTable1425 group by JoiningYear;
这将生成以下输出-
+-------------+----------+
| 加入年份 | count(*) |
+-------------+----------+
| 2000 | 3 |
| 2010 | 3 |
| 2015 | 1 |
+-------------+----------+
3行记录 (0.00 sec)
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