sql - SQL过程 - 根据其他表上的计数更改表列的值

Question

我有两张桌子，property和component。component.id_property = property.id.

我正在尝试创建一个过程，它计算所选属性上的组件，如果所选属性没有组件，它会更改property.id_state为 1。

create PROCEDURE property_statement_change AS
BEGIN
declare @value int;

select 
    @value = count(c.value)
from
    component c
where
    c.id_property = 1
group by c.id_property

IF (@value = 0)
  UPDATE property
  SET id_state = 1
  WHERE property.id = 1
END

如果我执行存储的产品，它不会改变任何东西，但选择和更新也可以正常工作。我做错了什么？

Answer 1

就像评论中所说的那样，值是 NULL 而不是 0，所以这里是代码：

create PROCEDURE property_statement_change AS
BEGIN
declare @value int;

select 
    @value = count(c.value)
from
    component c
where
    c.id_property = 1
group by c.id_property

IF (@value is NULL)
  UPDATE property
  SET id_state = 1
  WHERE property.id = 1
END