mysql多个字段拼接

Mysql的查询结果行字段拼接,可以用下面两个函数实现:

1. concat函数

mysql> select concat('','','') from test ;
+---------------------+
| concat('','','') |
+---------------------+
| 123 |
+---------------------+

如果连接串中存在NULL,则返回结果为NULL:

mysql> select concat('','',NULL,'') from test ;
+--------------------------+
| concat('','',NULL,'') |
+--------------------------+
| NULL |
+--------------------------+

2. concat_ws函数

concat(separator,str1,str2,...) 代表 concat with separator ,是concat()的特殊形式。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。

mysql> select concat_ws(':','','','') from test ;
+----------------------------+
| concat_ws(':','','','') |
+----------------------------+
| 1:2:3 |
+----------------------------+

分隔符为NULL,则返回结果为NULL:

mysql> select concat_ws(NULL,'','','') from test;
+-----------------------------+
| concat_ws(NULL,'','','') |
+-----------------------------+
| NULL |
+-----------------------------+

如果参数中存在NULL,则会被忽略:

mysql> select concat_ws(':','','',NULL,NULL,NULL,'') from test ;
+-------------------------------------------+
| concat_ws(':','','',NULL,NULL,NULL,'') |
+-------------------------------------------+
| 1:2:3 |
+-------------------------------------------+

可以对NULL进行判断,并用其它值进行替

mysql>  select concat_ws(':','','',ifNULL(NULL,''),'') from bank limit 1;
+---------------------------------------------+
| concat_ws(':','','',ifNULL(NULL,''),'') |
+---------------------------------------------+
| 1:2:0:3 |
+---------------------------------------------+
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