检查约束 - 在此上下文中不允许子查询

我累了添加检查约束，我到目前为止只失败了。

I tired to add a Check Constraint and I have only failed so far. What would be the way to get around this:

Msg 1046，Level 15，State 1，Line 6

Msg 1046, Level 15, State 1, Line 6

在此上下文中不允许使用子查询。只允许标量表达式
。

Subqueries are not allowed in this context. Only scalar expressions are allowed.

这是代码：

ALTER TABLE dbo.PropertySeasonDiscount ADD CONSTRAINT
[CC_PropertySeasonDiscount_MadeFrom_MadeTo]
CHECK (
    (SELECT COUNT(PropertySeasonDiscountId) FROM dbo.PropertySeasonDiscounts apsdeb 
        WHERE 
            (apsdeb.PropertySeasonId = PropertySeasonId) AND
            (
                (apsdeb.ValidForReservationsMadeTo >= ValidForReservationsMadeFrom AND ValidForReservationsMadeFrom >= apsdeb.ValidForReservationsMadeFrom) OR
                (apsdeb.ValidForReservationsMadeFrom <= ValidForReservationsMadeTo AND ValidForReservationsMadeTo <= apsdeb.ValidForReservationsMadeTo)
            )
    ) = 0
);