在Mysql 数据库中存在两种字符串连接操作.具体操作如下
一. 语法:
1. CONCAT(string1,string2,…) 说明 : string1,string2代表字符串,concat函数在连接字符串的时候，只要其中一个是NULL,那么将返回NULL
例1:
例2:
2. CONCAT_WS(separator,str1,str2,...)
说明 : string1,string2代表字符串,concat_ws 代表 concat with separator,第一个参数是其它参数的分隔符。分隔符的位置放在要连接的两个字符串之间。分隔符可以是一个字符串，也可以是其它参数。如果分隔符为 NULL，则结果为 NULL。函数会忽略任何分隔符参数后的 NULL 值。
举例1:
mysql> select concat_ws('#','dbdh=','NorthEastTrcoon',null) AS dbdh_name_three;
+-----------------------+| dbdh_name_three |+-----------------------+| dbdh=#NorthEastTrcoon |+-----------------------+1 row in set (0.00 sec)例2:
mysql> select concat_ws(null,'dbdh=','NorthEastTrcoon',null) AS dbdh_name_fourth
;+------------------+| dbdh_name_fourth |+------------------+| NULL |+------------------+1 row in set (0.00 sec)例3:
mysql> select concat_ws('*','dbdh=','NorthEastTrcoon',null) AS dbdh_name_fifth;
+-----------------------+| dbdh_name_fifth |+-----------------------+| dbdh=*NorthEastTrcoon |+-----------------------+1 row in set (0.00 sec)
3. MySQL中group_concat函数
完整的语法如下：group_concat([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])基本查询
mysql> select * from stu1;
+------+------+| id| name |+------+------+|1 | 10||1 | 20||1 | 20||2 | 20||3 | 200 ||3 | 500 |+------+------+6 rows in set (0.00 sec)以id分组，把name字段的值打印在一行，逗号分隔(默认)
mysql> select id,group_concat(name) from aa group by id;
+------+--------------------+| id| group_concat(name) |+------+--------------------+|1 | 10,20,20||2 | 20 ||3 | 200,500|+------+--------------------+3 rows in set (0.00 sec)以id分组，把name字段的值打印在一行，分号分隔
mysql> select id,group_concat(name separator ';') from aa group by id;
+------+----------------------------------+| id| group_concat(name separator ';') |+------+----------------------------------+|1 | 10;20;20 ||2 | 20||3 | 200;500 |+------+----------------------------------+3 rows in set (0.00 sec)以id分组，把去冗余的name字段的值打印在一行，
逗号分隔
mysql> select id,group_concat(distinct name) from aa group by id;
+------+-----------------------------+| id| group_concat(distinct name) |+------+-----------------------------+|1 | 10,20||2 | 20 ||3 | 200,500 |+------+-----------------------------+3 rows in set (0.00 sec)以id分组，把name字段的值打印在一行，逗号分隔，以name排倒序
mysql> select id,group_concat(name order by name desc) from aa group by id;
+------+---------------------------------------+| id| group_concat(name order by name desc) |+------+---------------------------------------+|1 | 20,20,10 ||2 | 20||3 | 500,200|+------+---------------------------------------+3 rows in set (0.00 sec)
还有一个简单的连接方式为: ||
mysql> select * from student;
+----+------+-------+----------+------------+| id | age | score | name | birth |+----+------+-------+----------+------------+| 1 | 23 | 78 | 李四 | 2017-10-10 || 2 | 24 | 78 | zhangsan | 2017-10-10 || 3 | 25 | 99 | 王五 | 2016-05-17 |+----+------+-------+----------+------------+3 rows in set (0.00 sec)mysql> select id+999,name,name+99,name+'999' from student;+--------+----------+---------+------------+| id+999 | name | name+99 | name+'999' |+--------+----------+---------+------------+| 1000 | 李四 | 99 | 999 || 1001 | zhangsan | 99 | 999 || 1002 | 王五 | 99 | 999 |+--------+----------+---------+------------+3 rows in set, 6 warnings (0.00 sec)