azure - Cosmos DB 左连接

Question

Cosmos DB 的所有文档，看起来它只支持 JOIN 关键字，这似乎是一种 INNER JOIN。

我有以下查询:

SELECT * FROM
(
    SELECT 
        DISTINCT(c.id),
        c.OtherCollection,
    FROM c
    JOIN s IN c.OtherCollection
)
AS c order by c.id

这工作正常并返回已填充 OtherCollection 的文档的数据。但它显然不会返回任何未填充的文档。

连接的原因是有时我会执行以下查询(查询是根据用户输入构建的)

SELECT * FROM
(
    SELECT 
        DISTINCT(c.id),
        c.OtherCollection,
    FROM c
    JOIN s IN c.OtherCollection
    WHERE s.PropertyName = 'SomeValue'
)
AS c order by c.id

问题是在这种情况下如何使用 LEFT JOIN 运算符？

Answer 1

您可以使用EXISTS语句模拟LEFT JOIN。 例如:

SELECT VALUE c 
FROM c
WHERE (
    (c.OtherCollection = null) OR EXISTS (--Like a "Left Join"
        SELECT null 
        FROM s IN c.OtherCollection
        WHERE s.PropertyName = 'SomeValue'
    )
)
--AND/OR Some other c Node conditions
order by c.id