在MongoDB中不存在右集合的地方,是否存在与左联接查询等效的查询?
SQL:
SELECT * FROM TableA as A LEFT JOIN TableB as B ON A.id = B.id
WHERE B.Id IS NULL
蒙古数据库:
???
附笔。:
我的初步草图:
db.getCollection('collA').aggregate([
{
$lookup:
{
from: "collB",
localField: "_id",
foreignField: "_id",
as: "collB"
}
}
//, {$match : collB is empty}
])
