加入子查询的所有结果

Question

所以我想 LEFT JOIN 至少被多个列之一引用的所有文件：

SELECT
    ...
FROM
    O o
    LEFT JOIN binary_stream_value bsv ON o.binary_stream_value_id = bsv.id
    LEFT JOIN artwork art ON o.artwork_id = art.id
    LEFT JOIN (SELECT f.id FROM file f WHERE f.id = bsv.file_id OR f.id = art.file_id) f ON TRUE
    ...

失败

ERROR:  invalid reference to FROM-clause entry for table "bsv"
LINE 212: ...  LEFT JOIN (SELECT f.id FROM file f WHERE f.id = bsv.file_i...
                                                               ^
HINT:  There is an entry for table "bsv", but it cannot be referenced from this part of the query.

诚然，我一半希望这会失败，一半希望我错了。

编写此类查询的正确方法是什么？

Answer 1

你需要一个横向连接来完成你想做的事情：

SELECT
    ...
FROM
    O o
    LEFT JOIN binary_stream_value bsv ON o.binary_stream_value_id = bsv.id
    LEFT JOIN artwork art ON o.artwork_id = art.id
    LEFT JOIN LATERAL (SELECT f.id FROM file f WHERE f.id = bsv.file_id OR f.id = art.file_id) f ON TRUE
    ...

但是子select并不是真正必要的开头：

SELECT
    ...
FROM
    O o
    LEFT JOIN binary_stream_value bsv ON o.binary_stream_value_id = bsv.id
    LEFT JOIN artwork art ON o.artwork_id = art.id
    LEFT JOIN file f on f.id = bsv.file_id OR f.id = art.file_id
    ...

加入子查询的所有结果

Join all results of a subquery

sql

postgresql

join

left-join

postgresql-9.6