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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('1','2','3') from test ;
+---------------------+
| concat('1','2','3') |
+---------------------+
| 123 |
+---------------------+
如果连接串中存在NULL，则返回结果为NULL：
mysql> select concat('1','2',NULL,'3') from test ;
+--------------------------+
| concat('1','2',NULL,'3') |
+--------------------------+
| NULL |
+--------------------------+ "2.concat_ws函数"
mysql> select concat_ws(':','1','2','3') from test ;
+----------------------------+
| concat_ws(':','1','2','3') |
+----------------------------+
| 1:2:3 |
+-------------------分隔符为NULL，则返回结果为NULL：
mysql> select concat_ws(NULL,'1','2','3') from test;
+-----------------------------+
| concat_ws(NULL,'1','2','3') |
+-----------------------------+
| NULL |
+-----------------------------+ 如果参数中存在NULL，则会被忽略：
mysql> select concat_ws(':','1','2',NULL,NULL,NULL,'3') from test ;
+-------------------------------------------+
| concat_ws(':','1','2',NULL,NULL,NULL,'3') |
+-------------------------------------------+
| 1:2:3 |
+-------------------------------------------+ 可以对NULL进行判断，并用其它值进行替换：
mysql> select concat_ws(':','1','2',ifNULL(NULL,'0'),'3') from bank limit 1;
+---------------------------------------------+
| concat_ws(':','1','2',ifNULL(NULL,'0'),'3') |
+---------------------------------------------+
| 1:2:0:3 |
+---------------------------------------------+ 
