MySQL查询以避免显示重复值？
为此，可以使用GROUPBY并使用COUNT来仅获取非重复值。以下是语法-
select yourColumnName from yourTableName group by yourColumnName having count(*)=1;
让我们首先创建一个表-
mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Subject varchar(100) -> );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable(Subject) values('MySQL');
mysql> insert into DemoTable(Subject) values('MongoDB');
mysql> insert into DemoTable(Subject) values('Java');
mysql> insert into DemoTable(Subject) values('MongoDB');
mysql> insert into DemoTable(Subject) values('C');
mysql> insert into DemoTable(Subject) values('C++');
mysql> insert into DemoTable(Subject) values('Java');
mysql> insert into DemoTable(Subject) values('C');使用select语句显示表中的所有记录-
mysql> select *from DemoTable;
输出结果
+----+---------+ | Id | Subject | +----+---------+ | 1 | MySQL | | 2 | MongoDB | | 3 | Java | | 4 | MongoDB | | 5 | C | | 6 | C++ | | 7 | Java | | 8 | C | +----+---------+ 8 rows in set (0.00 sec)
这是避免显示重复的查询-
mysql> select Subject from DemoTable group by Subject having count(*)=1;
输出结果
+---------+ | Subject | +---------+ | MySQL | | C++ | +---------+ 2 rows in set (0.00 sec)