T-SQL从不同的表中选择和计数？

Question

我有一个Threads包含字段(id)的table ().我想选择每一行Threads,以及表Posts中字段Posts.thread相同的行数Threads.id.

如何在SQL中完成？

(像这样的伪SQL: SELECT *, COUNT(* FROM Posts WHERE Posts.id=Threads.id) FROM Threads)

Answer 1

当然 - 这样的事情？

SELECT 
    t.ThreadID,
    (SELECT COUNT(*) FROM dbo.Posts p WHERE p.ThreadID = t.ThreadID)
FROM
    dbo.Threads t

Answer 2

SELECT t.id, COUNT(p.thread)
FROM Threads AS t
    LEFT OUTER JOIN Posts AS p
        ON t.id = p.thread
GROUP BY t.id