一、CONCAT(str1,str2,str3, …)
示例:
mysql> select concat("我愛你","何晶","一萬年");
+------------------------------------------+
| concat("我愛你","何晶","一萬年") |
+------------------------------------------+
| 我愛你何晶一萬年 |
+------------------------------------------+
1 row in set (0.00 sec)
mysql>
-- 拼接 null 字符串
mysql> select concat("我愛你","何晶","一萬年",'null');
+-------------------------------------------------+
| concat("我愛你","何晶","一萬年",'null') |
+-------------------------------------------------+
| 我愛你何晶一萬年null |
+-------------------------------------------------+
1 row in set (0.00 sec)
mysql>
-- 拼接 null
mysql> select concat("我愛你","何晶","一萬年",null);;;
+-----------------------------------------------+
| concat("我愛你","何晶","一萬年",null) |
+-----------------------------------------------+
| NULL |
+-----------------------------------------------+
1 row in set (0.00 sec)
mysql>
二、CONCAT_WS(separator,str1,str2,…)
說明 :
string1,string2代表字符串,concat_ws 代表 concat with separator,第一個參數是其它參數的分隔符。
分隔符的位置放在要連接的兩個字符串之間。
分隔符可以是一個字符串，也可以是其它參數。
如果分隔符爲 NULL，則結果爲 NULL。
函數會忽略任何分隔符參數後的 NULL 值
示例:
mysql> select concat_ws("何晶","我愛你","一萬年");
+---------------------------------------------+
| concat_ws("何晶","我愛你","一萬年") |
+---------------------------------------------+
| 我愛你何晶一萬年 |
+---------------------------------------------+
1 row in set (0.00 sec)
mysql>
-- 分隔符爲 null
mysql> select concat_ws(null,"我愛你何晶","一萬年");;;
+-----------------------------------------------+
| concat_ws(null,"我愛你何晶","一萬年") |
+-----------------------------------------------+
| NULL |
+-----------------------------------------------+
1 row in set (0.00 sec)
mysql>
-- 被拼接的字符串爲 null (null的位置不在第一位)
mysql> select concat_ws("一萬年","我愛你何晶",null);
+-----------------------------------------------+
| concat_ws("一萬年","我愛你何晶",null) |
+-----------------------------------------------+
| 我愛你何晶 |
+-----------------------------------------------+
1 row in set (0.00 sec)
mysql>
-- 被拼接的字符串爲 null (null的位置在第一位)
mysql> select concat_ws("一萬年",null,"我愛你何晶");
+-----------------------------------------------+
| concat_ws("一萬年",null,"我愛你何晶") |
+-----------------------------------------------+
| 我愛你何晶 |
+-----------------------------------------------+
1 row in set (0.00 sec)
mysql>
三、 MySQL中 GROUP_CONCAT 函數
完整語法
group_concat([DISTINCT] 要連接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])
示例：
-- 基礎查詢 sc表
mysql> select * from sc limit 10;
+-------+------+------+-------+
| sc_id | s_id | c_id | score |
+-------+------+------+-------+
| 1 | 1 | 1 | 23 |
| 2 | 1 | 2 | 93 |
| 3 | 1 | 3 | 55 |
| 4 | 1 | 4 | 96 |
| 5 | 1 | 5 | 15 |
| 6 | 1 | 6 | 88 |
| 7 | 1 | 7 | 91 |
| 8 | 1 | 8 | 94 |
| 9 | 1 | 9 | 95 |
| 10 | 1 | 10 | 92 |
+-------+------+------+-------+
10 rows in set (0.00 sec)
-- 以 c_id 分組，把 score 字段的值打印在一行，逗號分隔(默認)
mysql> select c_id,group_concat(score) from sc where sc_id < 20 group by c_id limit 10;
+------+---------------------+
| c_id | group_concat(score) |
+------+---------------------+
| 1 | 23,73 |
| 2 | 93,90 |
| 3 | 55,29 |
| 4 | 96,75 |
| 5 | 15,87 |
| 6 | 88,9 |
| 7 | 91,86 |
| 8 | 94,100 |
| 9 | 95,42 |
| 10 | 92 |
+------+---------------------+
10 rows in set (0.00 sec)
mysql>
-- 以 c_id 分組，把 score 字段的值打印在一行，分號分隔
mysql> select c_id,group_concat(score separator ";") from sc where sc_id < 20 group by c_id limit 10;
+------+-----------------------------------+
| c_id | group_concat(score separator ";") |
+------+-----------------------------------+
| 1 | 23;73 |
| 2 | 93;90 |
| 3 | 55;29 |
| 4 | 96;75 |
| 5 | 15;87 |
| 6 | 88;9 |
| 7 | 91;86 |
| 8 | 94;100 |
| 9 | 95;42 |
| 10 | 92 |
+------+-----------------------------------+
10 rows in set (0.00 sec)
mysql>
-- 以 sc_id 分組，把去冗餘的 score 字段的值打印在一行
mysql> select c_id,group_concat(distinct score) from sc where sc_id < 120 group by c_id limit 10;
+------+-------------------------------------+
| c_id | group_concat(distinct score) |
+------+-------------------------------------+
| 1 | 13,15,22,23,32,39,62,71,73,79,83,86 |
| 2 | 9,15,20,46,49,50,52,54,68,75,90,93 |
| 3 | 9,14,15,20,29,35,55,56,65,80,87,98 |
| 4 | 13,18,34,35,37,50,53,73,75,77,88,96 |
| 5 | 7,15,21,23,24,43,63,66,69,87 |
| 6 | 8,9,25,27,28,52,55,60,73,76,81,88 |
| 7 | 8,11,18,20,29,35,67,84,86,91,100 |
| 8 | 6,12,24,26,73,76,77,84,87,94,95,100 |
| 9 | 17,32,39,42,45,50,58,67,76,95,97 |
| 10 | 4,8,19,27,33,52,53,61,78,86,92 |
+------+-------------------------------------+
10 rows in set (0.00 sec)
mysql>
-- 以sc_id分組，把 score 字段的值打印在一行，逗號分隔，以 score 排倒序
mysql> select c_id,group_concat(score order by score desc) from sc where sc_id < 120 group by c_id;
+------+-----------------------------------------+
| c_id | group_concat(score order by score desc) |
+------+-----------------------------------------+
| 1 | 86,83,79,73,71,62,39,32,23,22,15,13 |
| 2 | 93,90,75,68,54,52,50,49,46,20,15,9 |
| 3 | 98,87,80,65,56,55,35,29,20,15,14,9 |
| 4 | 96,88,77,75,73,53,50,37,35,34,18,13 |
| 5 | 87,69,66,63,43,24,23,23,21,15,7,7 |
| 6 | 88,81,76,73,60,55,52,28,27,25,9,8 |
| 7 | 100,91,86,84,67,35,29,20,18,11,11,8 |
| 8 | 100,95,94,87,84,77,76,73,26,24,12,6 |
| 9 | 97,95,76,67,58,58,50,45,42,39,32,17 |
| 10 | 92,86,78,61,53,52,33,27,19,8,4 |
+------+-----------------------------------------+
10 rows in set (0.01 sec)
mysql>
四、直接 + (其實都不算是拼接了,算是相加)
示例：
mysql> select "n1m1"+999;
+------------+
| "n1m1"+999 |
+------------+
| 999 |
+------------+
1 row in set, 1 warning (0.00 sec)
mysql> select "n1m1"+"999";
+--------------+
| "n1m1"+"999" |
+--------------+
| 999 |
+--------------+
1 row in set, 1 warning (0.00 sec)
mysql> select "1"+"999";
+-----------+
| "1"+"999" |
+-----------+
| 1000 |
+-----------+
1 row in set (0.00 sec)
mysql> select 1+"999";
+---------+
| 1+"999" |
+---------+
| 1000 |
+---------+
1 row in set (0.00 sec)
mysql> select "asf"+"mimi";
+--------------+
| "asf"+"mimi" |
+--------------+
| 0 |
+--------------+
1 row in set, 2 warnings (0.00 sec)