我有桌子:
Project table
id name
-------
1 A
2 B
Assignment table
id name project_id
-------------------
1 A1 1
2 A2 1
3 A3 2
我希望编写一个查询,返回每个项目以及从中创建的作业的名称,例如:
project_id assignments
-----------------------
1 A1,A2
2 A3
有什么办法可以实现这一点吗?
您可以连接表并使用array_agg
组合以逗号分隔的值
SELECT a.id, array_agg(b.name) assignments
FROM Project a
INNER JOIN assignment b
ON a.id = b.project_ID
GROUP BY a.id
SQLFiddle 演示 http://sqlfiddle.com/#!1/df056/3
或通过使用STRING_AGG
SELECT a.id, STRING_AGG(b.name, ', ' ORDER BY b.name) assignments
FROM Project a
INNER JOIN assignment b
ON a.id = b.project_ID
GROUP BY a.id
SQLFiddle 演示 http://sqlfiddle.com/#!1/df056/5
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