我已经成功地实现了下面这个场景:
SELECT GROUP_CONCAT(coursecode)
FROM (
SELECT coursecode FROM Table18
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) <= 39
UNION
SELECT coursecode FROM Table17
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) <= 39
) s
WHERE coursecode
NOT IN (
SELECT coursecode
FROM Table18
WHERE regno = 'StudentXYZ'
AND (ca_score + exam_score) >= 40
UNION
SELECT coursecode
FROM Table17
WHERE regno = 'StudentXYZ'
AND (ca_score + exam_score) >= 40
)
这很好用! 以下是示例结果:
+----------------------------------------------------------------------------------------------------------+
| GROUP_CONCAT(coursecode) |
+----------------------------------------------------------------------------------------------------------+
| EDU222,EDU497,POS302,POS405,POS420,EDU224,EDU311,EDU312,EDU313,GST304,GST305,POS304,POS305,POS308,POS309 |
+----------------------------------------------------------------------------------------------------------+
但这就是我想要实现的:
+-------------------------------------------------+
| GROUP_CONCAT(coursecode) |
+-------------------------------------------------+
| EDU222, EDU497, POS302, POS405, POS420, EDU224, |
| EDU311, EDU312, EDU313, GST304, GST305, POS304, |
| POS305, POS308, POS309 |
+-------------------------------------------------+
有什么建议吗?或者更好的方法来解决这个挑战?
最佳答案
您可以执行如下操作(支持 MySQL 5.7/MariaDB < 10.2):
SELECT GROUP_CONCAT(coursecode)
FROM (
SELECT coursecode, @gn:=@gn+1, CEIL(@gn / 6) gn
FROM (
SELECT coursecode FROM Table18
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) <= 39
UNION
SELECT coursecode FROM Table17
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) <= 39
) s, (SELECT @gn:=0)gn
WHERE coursecode NOT IN (
SELECT coursecode
FROM Table18
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) >= 40
UNION
SELECT coursecode
FROM Table17
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) >= 40
)
) group_view GROUP BY group_view.gn
从 MySQL 8.0/MariaDB 10.2 开始,您可以使用相同的逻辑,但使用 ROW_NUMBER
而不是变量。所以你的查询可以是这样的:
SELECT GROUP_CONCAT(coursecode)
FROM (
SELECT coursecode, CEIL(ROW_NUMBER() OVER (ORDER BY code ASC) / 6) gn
FROM (
SELECT coursecode FROM Table18
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) <= 39
UNION
SELECT coursecode FROM Table17
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) <= 39
) s
WHERE coursecode NOT IN (
SELECT coursecode
FROM Table18
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) >= 40
UNION
SELECT coursecode
FROM Table17
WHERE regno = 'StudentXYZ' AND (ca_score + exam_score) >= 40
)
) group_view GROUP BY group_view.gn
关于mysql - 有没有更好的方法将 MySQL GROUP_CONCAT 输出拆分为多行?例如说每六 (6) 条记录后,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57482555/