关于Mysql group_concat的应用
■事先准备：
CREATE TABLE TBL_GRP_CAT (
ID INT,
VAL CHAR
);
INSERT INTO TBL_GRP_CAT VALUES(1, 'a');
INSERT INTO TBL_GRP_CAT VALUES(1, 'b');
INSERT INTO TBL_GRP_CAT VALUES(1, 'c');
INSERT INTO TBL_GRP_CAT VALUES(2, 'd');
INSERT INTO TBL_GRP_CAT VALUES(2, 'e');
INSERT INTO TBL_GRP_CAT VALUES(2, 'd');
INSERT INTO TBL_GRP_CAT VALUES(2, 'f');
mysql> select * from TBL_GRP_CAT;
+------+------+
| ID | VAL |
+------+------+
| 1 | a |
| 1 | b |
| 1 | c |
| 2 | d |
| 2 | e |
| 2 | d |
| 2 | f |
+------+------+
7 rows in set (0.00 sec)
mysql>
■语法：
group_concat([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])
■示例
示例1：把相同ID的VAL用逗号连接起来（可以重复）
SELECT ID, group_concat(VAL) VAL FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID;
mysql> SELECT ID, group_concat(VAL) VAL FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID
;
+------+---------+
| ID | VAL |
+------+---------+
| 1 | a,b,c |
| 2 | d,e,d,f |
+------+---------+
2 rows in set (0.00 sec)
mysql>
示例2：把相同ID的VAL用逗号连接起来（不含重复）
SELECT ID, group_concat(DISTINCT VAL) VAL FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID;
mysql> SELECT ID, group_concat(DISTINCT VAL) VAL FROM TBL_GRP_CAT GROUP BY ID OR
DER BY ID;
+------+-------+
| ID | VAL |
+------+-------+
| 1 | a,b,c |
| 2 | d,e,f |
+------+-------+
2 rows in set (0.00 sec)
mysql>
示例3：把相同ID的VAL由大到小用逗号连接起来（可以重复）
SELECT ID, group_concat(VAL Order BY VAL DESC) VAL FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID;
mysql> SELECT ID, group_concat(VAL Order BY VAL DESC) VAL FROM TBL_GRP_CAT GROU
BY ID ORDER BY ID;
+------+---------+
| ID | VAL |
+------+---------+
| 1 | c,b,a |
| 2 | f,e,d,d |
+------+---------+
2 rows in set (0.00 sec)
mysql>
示例4：把相同ID的VAL用字符'/'连接起来（可以重复）
SELECT ID, group_concat(VAL Separator '/') VAL FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID;
mysql> SELECT ID, group_concat(VAL Separator '/') VAL FROM TBL_GRP_CAT GROUP BY
ID ORDER BY ID;
+------+---------+
| ID | VAL |
+------+---------+
| 1 | a/b/c |
| 2 | d/e/d/f |
+------+---------+
2 rows in set (0.00 sec)
mysql>
示例5：权使用
SELECT ID, group_concat(DISTINCT VAL Order BY VAL DESC Separator '/') VAL FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID;
mysql> SELECT ID, group_concat(DISTINCT VAL Order BY VAL DESC Separator '/') VAL
FROM TBL_GRP_CAT GROUP BY ID ORDER BY ID;
+------+-------+
| ID | VAL |
+------+-------+
| 1 | c/b/a |
| 2 | f/e/d |
+------+-------+
2 rows in set (0.00 sec)
mysql>
在Oracle(Listagg)，Sqlite(group_concat)等均有类似功能。