使用 MySQL 查找重复项并显示在一行中
mysqlmysqli database更新于 2024/4/4 8:15:00
为此，您可以将 GROUP_CONCAT() 与 GROUP BY 子句一起使用。两者都用于对重复项进行分组并显示在一行中。让我们首先创建一个表 −
mysql> create table DemoTable ( StudentFavouriteSubject varchar(40), StudentName varchar(40) ) ; Query OK, 0 rows affected (0.75 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable values('MySQL','Chris');
Query OK, 1 row affected (0.22 sec)
mysql> insert into DemoTable values('MongoDB','Bob');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values('MySQL','Sam');
Query OK, 1 row affected (0.10 sec)
mysql> insert into DemoTable values('Java','Mike');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('C','Carol');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable values('MongoDB','John');
Query OK, 1 row affected (0.18 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+-------------------------+-------------+ | StudentFavouriteSubject | StudentName | +-------------------------+-------------+ | MySQL | Chris | | MongoDB | Bob | | MySQL | Sam | | Java | Mike | | C | Carol | | MongoDB | John | +-------------------------+-------------+ 6 rows in set (0.00 sec)
以下是查找重复项并显示在一行中的查询 −
mysql> select group_concat(StudentName),StudentFavouriteSubject from DemoTable group by StudentFavouriteSubject;
这将产生以下输出 −
+---------------------------+-------------------------+ | group_concat(StudentName) | StudentFavouriteSubject | +---------------------------+-------------------------+ | Carol | C | | Mike | Java | | Bob,John | MongoDB | | Chris,Sam | MySQL | +---------------------------+-------------------------+ 4 rows in set (0.00 sec)
