一、concat函數(shù)相關(guān)的幾種用法
1-1、函數(shù)：concat(str1,str2,…)
concat 函數(shù)一般用在SELECT 查詢語(yǔ)法中，用于修改返回字段內(nèi)容，例如有張LOL英雄信息表如下
mysql> select * from `LOL`;
+----+---------------+--------------+-------+
| id | hero_title | hero_name | price |
+----+---------------+--------------+-------+
| 1 | D刀鋒之影 | 泰隆 | 6300 |
| 2 | X迅捷斥候 | 提莫 | 6300 |
| 3 | G光輝女郎 | 拉克絲 | 1350 |
| 4 | F發(fā)條魔靈 | 奧莉安娜 | 6300 |
| 5 | Z至高之拳 | 李青 | 6300 |
| 6 | W無(wú)極劍圣 | 易 | 450 |
| 7 | J疾風(fēng)劍豪 | 亞索 | 450 |
+----+---------------+--------------+-------+
7 rows in set (0.00 sec)
我需要返回一列：英雄稱號(hào) - 英雄名稱 的數(shù)據(jù)，這是就用到了concat函數(shù)，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刀鋒之影 - 泰隆 | 6300 |
| X迅捷斥候 - 提莫 | 6300 |
| G光輝女郎 - 拉克絲 | 1350 |
| F發(fā)條魔靈 - 奧莉安娜 | 6300 |
| Z至高之拳 - 李青 | 6300 |
| W無(wú)極劍圣 - 易 | 450 |
| J疾風(fēng)劍豪 - 亞索 | 450 |
+------------------------------+-------+
7 rows in set (0.00 sec)
如果拼接的參數(shù)中有NULL，則返回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刀鋒之影NULL泰隆 | 6300 |
| X迅捷斥候NULL提莫 | 6300 |
| G光輝女郎NULL拉克絲 | 1350 |
| F發(fā)條魔靈NULL奧莉安娜 | 6300 |
| Z至高之拳NULL李青 | 6300 |
| W無(wú)極劍圣NULL易 | 450 |
| J疾風(fēng)劍豪NULL亞索 | 450 |
+-------------------------------+-------+
7 rows in set (0.00 sec)
image.png
不好意思，上面是我弟弟寫的，正確的如下：
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、函數(shù)：concat_ws(separator,str1,str2,…)
CONCAT_WS() 函數(shù)全稱： CONCAT With Separator ，是CONCAT()的特殊形式。第一個(gè)參數(shù)（separator）是其它參數(shù)的分隔符。分隔符的位置在要連接的兩個(gè)字符串之間。分隔符可以是一個(gè)字符串，也可以是其它字段參數(shù)。
需要注意的是：
如果分隔符為 NULL，則結(jié)果為 NULL；但如果分隔符后面的參數(shù)為NULL，只會(huì)被直接忽略掉，而不會(huì)導(dǎo)致結(jié)果為NULL。
好了，我們依舊用上面的LOL表，連接各字段，以逗號(hào)分隔：
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刀鋒之影,泰隆,6300 | 6300 |
| X迅捷斥候,提莫,6300 | 6300 |
| G光輝女郎,拉克絲,1350 | 1350 |
| F發(fā)條魔靈,奧莉安娜,6300 | 6300 |
| Z至高之拳,李青,6300 | 6300 |
| W無(wú)極劍圣,易,450 | 450 |
| J疾風(fēng)劍豪,亞索,450 | 450 |
+---------------------------------+-------+
7 rows in set (0.00 sec)
分隔符后的拼接參數(shù)為NULL時(shí)，直接忽略，不會(huì)影響整體結(jié)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刀鋒之影,泰隆 | 6300 |
| X迅捷斥候,提莫 | 6300 |
| G光輝女郎,拉克絲 | 1350 |
| F發(fā)條魔靈,奧莉安娜 | 6300 |
| Z至高之拳,李青 | 6300 |
| W無(wú)極劍圣,易 | 450 |
| J疾風(fēng)劍豪,亞索 | 450 |
+----------------------------+-------+
7 rows in set (0.00 sec)
分隔符為NULL時(shí)，結(jié)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、函數(shù)：group_concat(expr)
group_concat ( [DISTINCT] 字段名 [order by 排序字段 ASC/DESC] [Separator ‘分隔符’] )
group_concat函數(shù)通常用于有g(shù)roup by的查詢語(yǔ)句，group_concat一般包含在查詢返回結(jié)果字段中。
是不是group_concat函數(shù)的公式看著還挺復(fù)雜的？我們一起看看，上方公式中 [] 括號(hào)是可選項(xiàng)，表示可用可不用；
- 1.
[DISTINCT]：對(duì)拼接的參數(shù)支持去重功能； - 2.
[Order by]：拼接的參數(shù)支持排序功能； - 3.
[Separator]：這個(gè)你很熟悉了，支持自定義’分隔符’，如不設(shè)置默認(rèn)為無(wú)分隔符；
好了，下面讓我們來(lái)進(jìn)入開(kāi)心的測(cè)試環(huán)節(jié)吧~ 還是用這張LOL表，別問(wèn)為什么?；蛟S這就是青春吧！還記的那年通宵五排，大龍團(tuán)的時(shí)候網(wǎng)吧停電了…
[圖片上傳失敗...(image-263d78-1605259232468)]
又跑題了。。不好意思。
mysql> select * from `LOL`;
+----+---------------+--------------+-------+
| id | hero_title | hero_name | price |
+----+---------------+--------------+-------+
| 1 | D刀鋒之影 | 泰隆 | 6300 |
| 2 | X迅捷斥候 | 提莫 | 6300 |
| 3 | G光輝女郎 | 拉克絲 | 1350 |
| 4 | F發(fā)條魔靈 | 奧莉安娜 | 6300 |
| 5 | Z至高之拳 | 李青 | 6300 |
| 6 | W無(wú)極劍圣 | 易 | 450 |
| 7 | J疾風(fēng)劍豪 | 亞索 | 450 |
+----+---------------+--------------+-------+
7 rows in set (0.00 sec)
舉個(gè)場(chǎng)景，我們要區(qū)分出各個(gè)價(jià)格段的英雄來(lái)，如果不用group_concat的話，或許只能用order by區(qū)分了。
select * from `LOL` order by price desc;
mysql> select * from `LOL` order by price desc;
+----+---------------+--------------+-------+
| id | hero_title | hero_name | price |
+----+---------------+--------------+-------+
| 1 | D刀鋒之影 | 泰隆 | 6300 |
| 2 | X迅捷斥候 | 提莫 | 6300 |
| 4 | F發(fā)條魔靈 | 奧莉安娜 | 6300 |
| 5 | Z至高之拳 | 李青 | 6300 |
| 3 | G光輝女郎 | 拉克絲 | 1350 |
| 6 | W無(wú)極劍圣 | 易 | 450 |
| 7 | J疾風(fēng)劍豪 | 亞索 | 450 |
+----+---------------+--------------+-------+
7 rows in set (0.00 sec)
但是這樣很不直觀啊，我想一行都看到，怎么辦？
SELECT GROUP_CONCAT(hero_title,' - ',hero_name Separator ',' ) as full_name, price
from `LOL` GROUP BY price ORDER BY price desc;
這時(shí)GROUP_CONCAT函數(shù)就輕松的幫你解決了這個(gè)問(wèn)題?？?，舒服不~
注釋：這里我是拼接了（hero_title,’ - ‘,hero_name）這三個(gè)參數(shù)，分隔符設(shè)為：’,’，根據(jù)價(jià)格來(lái)分組，根據(jù)價(jià)格來(lái)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刀鋒之影 - 泰隆,X迅捷斥候 - 提莫,F發(fā)條魔靈 - 奧莉安娜,Z至高之拳 - 李青 | 6300 |
| G光輝女郎 - 拉克絲 | 1350 |
| W無(wú)極劍圣 - 易,J疾風(fēng)劍豪 - 亞索 | 450 |
+------------------------------------------------------------------------+-------+
3 rows in set (0.00 sec)
如果按價(jià)格（price）從小到大排序，只需控制外層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無(wú)極劍圣 - 易,J疾風(fēng)劍豪 - 亞索 | 450 |
| G光輝女郎 - 拉克絲 | 1350 |
| D刀鋒之影 - 泰隆,X迅捷斥候 - 提莫,F發(fā)條魔靈 - 奧莉安娜,Z至高之拳 - 李青 | 6300 |
+-------------------------------------------------------------------------+-------+
3 rows in set (0.00 sec)
那么GROUP_CONCAT函數(shù)中的order by 排序怎么用？是用在了拼接字段的排序上，如根據(jù)hero_title進(jìn)行排序拼接，如下：
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疾風(fēng)劍豪 - 亞索,W無(wú)極劍圣 - 易 | 450 |
| G光輝女郎 - 拉克絲 | 1350 |
| D刀鋒之影 - 泰隆,F發(fā)條魔靈 - 奧莉安娜,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拼接函數(shù)還是很好用的，希望你在有類似的需求或困惑時(shí)，想到它！或者能找到這篇博客，幫到你！
