group_concat
description
Syntax
VARCHAR GROUP_CONCAT([DISTINCT] VARCHAR str[, VARCHAR sep] [ORDER BY { col_name | expr} [ASC | DESC])
该函数是类似于 sum() 的聚合函数，group_concat 将结果集中的多行结果连接成一个字符串。第二个参数 sep 为字符串之间的连接符号，该参数可以省略，并支持Order By进行多行结果的排序，排序和聚合列可不同。该函数通常需要和 group by 语句一起使用。
example
mysql> select value from test;
+-------+
| value |
+-------+
| a |
| b |
| c |
| c |
+-------+
mysql> select GROUP_CONCAT(value) from test;
+-----------------------+
| GROUP_CONCAT(`value`) |
+-----------------------+
| a, b, c, c |
+-----------------------+
mysql> select GROUP_CONCAT(DISTINCT value) from test;
+-----------------------+
| GROUP_CONCAT(`value`) |
+-----------------------+
| a, b, c |
+-----------------------+
mysql> select GROUP_CONCAT(value, " ") from test;
+----------------------------+
| GROUP_CONCAT(`value`, ' ') |
+----------------------------+
| a b c c |
+----------------------------+
mysql> select GROUP_CONCAT(value, NULL) from test;
+----------------------------+
| GROUP_CONCAT(`value`, NULL)|
+----------------------------+
| NULL |
+----------------------------+
SELECT abs(k3), group_concat(distinct cast(abs(k2) as varchar) order by abs(k1), k5) FROM bigtable group by abs(k3) order by abs(k3); +------------+-------------------------------------------------------------------------------+
| abs(`k3`) | group_concat(DISTINCT CAST(abs(`k2`) AS CHARACTER), ORDER BY abs(`k1`), `k5`) |
+------------+-------------------------------------------------------------------------------+
| 103 | 255 |
| 1001 | 1989, 1986 |
| 1002 | 1989, 32767 |
| 3021 | 1991, 32767, 1992 |
| 5014 | 1985, 1991 |
| 25699 | 1989 |
| 2147483647 | 255, 1991, 32767, 32767 |
+------------+-------------------------------------------------------------------------------+keywords
GROUP_CONCAT,GROUP,CONCAT