选择不存在的所有对象值

Question

我有两个表： 对象object_id列 和具有object_id（FK for object.object_id）和value_type（为了简单起见，我ommited其他列）avalues。

我想选择所有没有指定类型值的对象。我的选择是这样的：

SELECT object_id FROM object WHERE NOT EXISTS (SELECT true FROM avalues v WHERE v.value_type = 10 and v.object_id = object_id); 

有没有更有效的方法来做到这一点？

Answer 1

NOT IN和LEFT JOIN/IS NULL稍微更高效：

SELECT object_id 
FROM object 
WHERE object_id NOT IN 
     (
     SELECT object_id 
     FROM avalues v 
     WHERE v.value_type = 10 
     ) 

或

SELECT o.object_id 
FROM object o 
LEFT JOIN 
     avalues v 
ON  v.object_id = o.object_id 
     AND v.value_type = 10 
WHERE v.object_id IS NULL 

请确保您有avalues (object_id, value_type)