前几篇文章给大家介绍了MySQL中的替换函数（Replace）、切分函数（SubString），今天我们一起来看看MySQL专业拼接“字符串”的函数：concat。老规矩，有好的建议和想法，记得写到评论中，等我上班摸鱼时，跟大家一起吃瓜~
一、concat函数相关的几种用法
1-1、函数：concat(str1,str2,…)
concat 函数一般用在SELECT 查询语法中，用于修改返回字段内容，例如有张LOL英雄信息表如下
mysql> select * from `LOL`; +----+---------------+--------------+-------+ | id | hero_title | hero_name | price | +----+---------------+--------------+-------+ | 1 | D刀锋之影 | 泰隆 | 6300 | | 2 | X迅捷斥候 | 提莫 | 6300 | | 3 | G光辉女郎 | 拉克丝 | 1350 | | 4 | F发条魔灵 | 奥莉安娜 | 6300 | | 5 | Z至高之拳 | 李青 | 6300 | | 6 | W无极剑圣 | 易 | 450 | | 7 | J疾风剑豪 | 亚索 | 450 | +----+---------------+--------------+-------+ 7 rows in set (0.00 sec)
我需要返回一列：英雄称号 - 英雄名称 的数据，这是就用到了concat函数，如下：
SELECT CONCAT(hero_title,' - ',hero_name) as full_name, price from `LOL`;
mysql> SELECT CONCAT(hero_title,' - ',hero_name) as full_name, price from `LOL`; +------------------------------+-------+ | full_name | price | +------------------------------+-------+ | D刀锋之影 - 泰隆 | 6300 | | X迅捷斥候 - 提莫 | 6300 | | G光辉女郎 - 拉克丝 | 1350 | | F发条魔灵 - 奥莉安娜 | 6300 | | Z至高之拳 - 李青 | 6300 | | W无极剑圣 - 易 | 450 | | J疾风剑豪 - 亚索 | 450 | +------------------------------+-------+ 7 rows in set (0.00 sec)
如果拼接的参数中有NULL，则返回NULL；如下：
SELECT CONCAT(hero_title,NULL,hero_name) as full_name, price from `LOL`;
mysql> SELECT CONCAT(hero_title,'NULL',hero_name) as full_name, price from `LOL`; +-------------------------------+-------+ | full_name | price | +-------------------------------+-------+ | D刀锋之影NULL泰隆 | 6300 | | X迅捷斥候NULL提莫 | 6300 | | G光辉女郎NULL拉克丝 | 1350 | | F发条魔灵NULL奥莉安娜 | 6300 | | Z至高之拳NULL李青 | 6300 | | W无极剑圣NULL易 | 450 | | J疾风剑豪NULL亚索 | 450 | +-------------------------------+-------+ 7 rows in set (0.00 sec)
不好意思，上面是我弟弟写的，正确的如下：
mysql> SELECT CONCAT(hero_title,NULL,hero_name) as full_name, price from `LOL`; +-----------+-------+ | full_name | price | +-----------+-------+ | NULL | 6300 | | NULL | 6300 | | NULL | 1350 | | NULL | 6300 | | NULL | 6300 | | NULL | 450 | | NULL | 450 | +-----------+-------+ 7 rows in set (0.00 sec)
1-2、函数：concat_ws(separator,str1,str2,…)
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select concat_ws(',',hero_title,hero_name,price) as full_name, price from `LOL`;
mysql> select concat_ws(',',hero_title,hero_name,price) as full_name, price from `LOL`;
+---------------------------------+-------+
| full_name | price |
+---------------------------------+-------+
| D刀锋之影,泰隆,6300 | 6300 |
| X迅捷斥候,提莫,6300 | 6300 |
| G光辉女郎,拉克丝,1350 | 1350 |
| F发条魔灵,奥莉安娜,6300 | 6300 |
| Z至高之拳,李青,6300 | 6300 |
| W无极剑圣,易,450 | 450 |
| J疾风剑豪,亚索,450 | 450 |
+---------------------------------+-------+
7 rows in set (0.00 sec)
分隔符后的拼接参数为NULL时，直接忽略，不会影响整体结果，如下：
select concat_ws(',',hero_title,NULL,hero_name) as full_name, price from `LOL`;
mysql> select concat_ws(',',hero_title,NULL,hero_name) as full_name, price from `LOL`;
+----------------------------+-------+
| full_name | price |
+----------------------------+-------+
| D刀锋之影,泰隆 | 6300 |
| X迅捷斥候,提莫 | 6300 |
| G光辉女郎,拉克丝 | 1350 |
| F发条魔灵,奥莉安娜 | 6300 |
| Z至高之拳,李青 | 6300 |
| W无极剑圣,易 | 450 |
| J疾风剑豪,亚索 | 450 |
+----------------------------+-------+
7 rows in set (0.00 sec)
分隔符为NULL时，结果返回NULL，如下：
select concat_ws(NULL,hero_title,hero_name,price) as full_name, price from `LOL`;
mysql> select concat_ws(NULL,hero_title,hero_name,price) as full_name, price from `LOL`; +-----------+-------+ | full_name | price | +-----------+-------+ | NULL | 6300 | | NULL | 6300 | | NULL | 1350 | | NULL | 6300 | | NULL | 6300 | | NULL | 450 | | NULL | 450 | +-----------+-------+ 7 rows in set (0.00 sec)
1-3、函数：group_concat(expr)
group_concat ( [DISTINCT] 字段名 [order by 排序字段 ASC/DESC] [Separator ‘分隔符'] )
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又跑题了。。不好意思。
mysql> select * from `LOL`; +----+---------------+--------------+-------+ | id | hero_title | hero_name | price | +----+---------------+--------------+-------+ | 1 | D刀锋之影 | 泰隆 | 6300 | | 2 | X迅捷斥候 | 提莫 | 6300 | | 3 | G光辉女郎 | 拉克丝 | 1350 | | 4 | F发条魔灵 | 奥莉安娜 | 6300 | | 5 | Z至高之拳 | 李青 | 6300 | | 6 | W无极剑圣 | 易 | 450 | | 7 | J疾风剑豪 | 亚索 | 450 | +----+---------------+--------------+-------+ 7 rows in set (0.00 sec)
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select * from `LOL` order by price desc;
mysql> select * from `LOL` order by price desc; +----+---------------+--------------+-------+ | id | hero_title | hero_name | price | +----+---------------+--------------+-------+ | 1 | D刀锋之影 | 泰隆 | 6300 | | 2 | X迅捷斥候 | 提莫 | 6300 | | 4 | F发条魔灵 | 奥莉安娜 | 6300 | | 5 | Z至高之拳 | 李青 | 6300 | | 3 | G光辉女郎 | 拉克丝 | 1350 | | 6 | W无极剑圣 | 易 | 450 | | 7 | J疾风剑豪 | 亚索 | 450 | +----+---------------+--------------+-------+ 7 rows in set (0.00 sec)
但是这样很不直观啊，我想一行都看到，怎么办？
SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price desc;
这时GROUP_CONCAT函数就轻松的帮你解决了这个问题。看，舒服不~
注释：这里我是拼接了（hero_title,' - ‘,hero_name）这三个参数，分隔符设为：','，根据价格来分组，根据价格来排的序。效果如下
mysql> SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price desc; +------------------------------------------------------------------------+-------+ | full_name | price | +------------------------------------------------------------------------+-------+ | D刀锋之影 - 泰隆,X迅捷斥候 - 提莫,F发条魔灵 - 奥莉安娜,Z至高之拳 - 李青 | 6300 | | G光辉女郎 - 拉克丝 | 1350 | | W无极剑圣 - 易,J疾风剑豪 - 亚索 | 450 | +------------------------------------------------------------------------+-------+ 3 rows in set (0.00 sec)
如果按价格（price）从小到大排序，只需控制外层ORDER BY即可，如下：
SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc;
mysql> SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc; +-------------------------------------------------------------------------+-------+ | full_name | price | +-------------------------------------------------------------------------+-------+ | W无极剑圣 - 易,J疾风剑豪 - 亚索 | 450 | | G光辉女郎 - 拉克丝 | 1350 | | D刀锋之影 - 泰隆,X迅捷斥候 - 提莫,F发条魔灵 - 奥莉安娜,Z至高之拳 - 李青 | 6300 | +-------------------------------------------------------------------------+-------+ 3 rows in set (0.00 sec)
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SELECT GROUP_CONCAT(hero_title,' - ',hero_name order by hero_title Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc;
mysql> SELECT GROUP_CONCAT(hero_title,' - ',hero_name order by hero_title Separator ',' ) as full_name, price from `LOL` GROUP BY price ORDER BY price asc; +-------------------------------------------------------------------------+-------+ | full_name | price | +-------------------------------------------------------------------------+-------+ | J疾风剑豪 - 亚索,W无极剑圣 - 易 | 450 | | G光辉女郎 - 拉克丝 | 1350 | | D刀锋之影 - 泰隆,F发条魔灵 - 奥莉安娜,X迅捷斥候 - 提莫,Z至高之拳 - 李青 | 6300 | +-------------------------------------------------------------------------+-------+ 3 rows in set (0.00 sec)
好了，可以看出，MySQL中的concat拼接函数还是很好用的，希望你在有类似的需求或困惑时，想到它！或者能找到这篇博客，帮到你！
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