如果其他表中的结果大于 n，SQLite 选择

Question

我的数据库中有以下表格：

sessions                 measurements
--------                 ------------
id                       id
etc.                     session_id
                         etc.

我想做类似的事情

SELECT * FROM sessions IF 
   (measurements HAS MORE THAN 0 RESULTS WHERE session_id=X)

Is this sort of query possible in sqlite?

此致

Answer 1

我不确定 SQLite 是否支持 EXISTS，所以我提供了两种选择：

SELECT *
FROM sessions S
WHERE EXISTS (SELECT 1 FROM measurements WHERE session_is = S.id)

或者

SELECT *
FROM sessions S
WHERE (SELECT COUNT(*) FROM measurements WHERE session_is = S.id) > 0

Answer 2

这将做到这一点：

select * from sessions where (select count(*) from measurements where session_id=X)>0