问题
I have two tables named Districts and Schools. The Districts table contains a column named Schools.
I need to populate the Schools column of the Districts table from the corresponding Schools table, so that each row in the Districts table has a comma separated list of values of school names from the Schools table.
How can I do this? Should I use an UPDATE query or a stored procedure?
I only got as far as:
SQL Fiddle
Districts Table
+------------+------+---------+
| DistrictId | Name | Schools |
+------------+------+---------+
| 1 | a | |
| 2 | b | |
| 3 | c | |
| 4 | d | |
+------------+------+---------+
Schools Table
+----------+------------+------------+
| SchoolId | SchoolName | DistrictId |
+----------+------------+------------+
| 1 | s1 | 1 |
| 2 | s2 | 1 |
| 3 | s3 | 2 |
| 4 | s4 | 2 |
| 5 | s5 | 4 |
+----------+------------+------------+
How the Output Needs to be
+------------+------+---------+
| DistrictId | Name | Schools |
+------------+------+---------+
| 1 | a | s1,s2 |
| 2 | b | s3,s4 |
| 3 | c | |
| 4 | d | s5 |
+------------+------+---------+
回答1:
With the help of FOR XML PATH and STUFF to CONCATENATE the values, you can easily update the table District with your desired result.
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
来源：https://stackoverflow.com/questions/15524457/update-a-database-table-field-with-comma-separated-list-from-join