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法律研究仅显示出现在 MySQL 中至少三次以上的重复列名称
为此请使用 HAVING COUNT()。我们先创建一个表 -
mysql> create table DemoTable1351 -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(40) -> ); Query OK, 0 rows affected (1.08 sec)
使用插入命令向表中插入一些记录 -
mysql> insert into DemoTable1351(StudentName) values('Chris');
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable1351(StudentName) values('Bob');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1351(StudentName) values('Bob');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1351(StudentName) values('David');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1351(StudentName) values('Bob');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1351(StudentName) values('David');
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable1351(StudentName) values('Bob');
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable1351(StudentName) values('Mike');
Query OK, 1 row affected (0.68 sec)
mysql> insert into DemoTable1351(StudentName) values('David');
Query OK, 1 row affected (0.12 sec)使用 select 语句从表中显示所有记录 -
mysql> select * from DemoTable1351;
这会生成以下输出 -
+-----------+-------------+ | StudentId | StudentName | +-----------+-------------+ | 1 | Chris | | 2 | Bob | | 3 | Bob | | 4 | David | | 5 | Bob | | 6 | David | | 7 | Bob | | 8 | Mike | | 9 | David | +-----------+-------------+ 9 rows in set (0.00 sec)
以下是对出现在至少三次的重复列名称的显示查询 -
mysql> select * from DemoTable1351 -> group by StudentName -> having count(StudentName) >=3;
这会生成以下输出 -
+-----------+-------------+ | StudentId | StudentName | +-----------+-------------+ | 2 | Bob | | 4 | David | +-----------+-------------+ 2 rows in set (0.00 sec)
更新于： 2019-11-05
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