sql - 使用来自连接的逗号分隔列表更新数据库表字段

Question

我有两个名为 Districts 和 Schools 的表。 Districts 表包含一个名为 Schools 的列。

我需要从相应的 Schools 表中填充 Districts 表的 Schools 列，以便 中的每一行Districts 表有一个逗号分隔的列表，其中列出了 Schools 表中的学校名称值。

我该怎么做？我应该使用 UPDATE 查询还是存储过程？

我只得到了:

SQL Fiddle

地区表

+------------+------+---------+
| DistrictId | Name | Schools |
+------------+------+---------+
|          1 | a    |         |
|          2 | b    |         |
|          3 | c    |         |
|          4 | d    |         |
+------------+------+---------+

学校表

+----------+------------+------------+
| SchoolId | SchoolName | DistrictId |
+----------+------------+------------+
|        1 | s1         |          1 |
|        2 | s2         |          1 |
|        3 | s3         |          2 |
|        4 | s4         |          2 |
|        5 | s5         |          4 |
+----------+------------+------------+

输出需要如何

+------------+------+---------+
| DistrictId | Name | Schools |
+------------+------+---------+
|          1 | a    | s1,s2   |
|          2 | b    | s3,s4   |
|          3 | c    |         |
|          4 | d    | s5      |
+------------+------+---------+

Answer 1

借助 FOR XML PATH 和 STUFF 要连接这些值，您可以轻松地使用所需的结果更新表District。

UPDATE  a
SET     a.Schools = b.SchoolList
FROM    Districts a
        INNER JOIN
        (
            SELECT  DistrictId,
                    STUFF((SELECT ', ' + SchoolName
                            FROM Schools
                            WHERE DistrictId = a.DistrictId
                            FOR XML PATH (''))
                        , 1, 1, '')  AS SchoolList
            FROM    Districts AS a
            GROUP   BY DistrictId
        ) b ON A.DistrictId = b.DistrictId
WHERE   b.SchoolList IS NOT NULL

• SQLFiddle Demo