RethinkDB - 左联接，joined_table.identifier 为空? [英] RethinkDB - Left join where joined_table.identifier is null?

问题描述

我在 RethinkDB 数据库中有两个表，它们表示一对多关系.考虑以下两个表:

I have two tables in a RethinkDB database that represent a one-to-many relationship. Consider the following two tables:

t1
ParentId    Name
1           lorem
2           ipsum
3           dotor
4           sit
5           amet

t2
ChildId ParentId    ChildName
1       1           something
2       3           random
3       5           here

在 t1 上，ParentId 是主键，在 t2 上，ParentId 上有一个二级索引.我想找出哪些父母没有孩子.SQL(确切地说是 MSSQL)中的操作如下所示:

On t1, ParentId is the primary key, and on t2, there is a secondary index on ParentId. I want to find which parents don't have a child. The operation in SQL (MSSQL to be exact) looks like this:

SELECT t1.*
FROM t1
LEFT OUTER JOIN t2 ON t2.ParentId = t1.ParentId
WHERE t2.ChildId IS NULL

Results:
ParentId    Name
2           ipsum
4           sit

如何在 RethinkDB 中实现类似的结果?谢谢！

How can I accomplish this similar result in RethinkDB? Thank you!

推荐答案

我会这样做:

r.table('t1').filter(function(parent) {
  return r.table('t2').get_all(parent('ParentId'), {index: 'ParentId'}).count().eq(0);
})

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