Question

我有WHERE子句条件涉及ALL子查询。有时子查询结果为空，在这种情况下，表达式始终计算为true，但我希望它评估为false。

例如，假设我有一个驱动程序表，一个路由表和一个多对多交互表，显示每个驱动程序驱动的路由。我想找到驾驶路线超过50英里的司机。

SELECT * FROM driver 
WHERE 50 < ALL(
    SELECT miles FROM route, driver_route
    WHERE driver_route.route_id = route.id AND
          driver_route.driver_id = driver.id)

此查询将包括未在结果中驱动任何路由的驱动程序，这不是我想要的。

我尝试过使用coalesce，但遇到了ERROR: more than one row returned by a subquery used as an expression。以下是我对该查询的措辞：

SELECT * FROM driver 
WHERE 50 < COALESCE((
    SELECT ALL(SELECT miles FROM route, driver_route 
    WHERE driver_route.route_id = route.id AND 
          driver_route.driver_id = driver.id)), 
    0);

我正在寻找一种足以应用于不同类型和查询的结构。

Answer 1

我认为你需要这个：

select driver.* from driver inner join (
    select driver.id  from driver
    inner join driver_route 
    on driver.id = driver_route.driver_id
    inner join route
    on route.id = driver_route.route_id
    group by driver.id 
    having min(route.miles) > 50
)t 
on driver.id = t.id

Answer 2

这个怎么样？

SELECT * FROM driver  
WHERE NOT EXISTS (  
    SELECT miles FROM route, driver_route  
    WHERE driver_route.route_id = route.id AND  
          driver_route.driver_id = driver.id AND   
          miles <= 50  
                 )  
 AND EXISTS (  
    SELECT miles FROM route, driver_route  
    WHERE driver_route.route_id = route.id AND  
          driver_route.driver_id = driver.id AND  
          miles > 50  
                 )

全部大于50等于没有小于或等于50。

postgresql ALL子查询将empty计算为true

2 个答案: