Question

我有两张桌子：具有object_id列的对象和具有object_id（对象为object.object_id的FK）和value_type的avalues（为简单起见，我省略了其他列）。

我想选择所有没有指定类型值的对象。我的选择看起来像这样：

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

有更有效的方法吗？

Answer 1

NOT IN和LEFT JOIN / IS NULL稍微提高效率：

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

确保您在avalues (object_id, value_type)

上有索引

选择不存在值的所有对象

1 个答案: