合并时指定的非布尔类型的表达式？

Question

我有以下代码来创建存储过程，但我似乎在这一行下面遇到了很多错误：

ON (Target.Email = Source.Email AND Target.PromoName = Source.PromoName)

此行的错误是＃34;指定非布尔类型的表达式＆＃34;。 我在这里做错了什么？

CREATE PROCEDURE [dbo].InsertUpdateBasicPromoEntry
    @Email nvarchar(100)
    ,@PromoName varchar(100)
    ,@MaxEntries tinyint
AS
BEGIN
    SET NOCOUNT ON;

    MERGE [dbo].[BasicCodePromoEntries] AS Target
    USING (
        SELECT 
            @Email as Email
        ,@PromoName as PromoName
    ) AS Source
    ON (Target.Email = Source.Email AND Target.PromoName = Source.PromoName)
    WHEN MATCHED
    THEN
        BEGIN
        IF Target.PeriodExpires < GETDATE()
            BEGIN
                UPDATE SET 
                    Target.PeriodExpires = GETDATE()
                    ,Target.PeriodEntries = 1
            END
        ELSE IF Target.PeriodExpires > GETDATE() AND Target.PeriodEntries < @MaxEntries
            BEGIN
                UPDATE SET
                    Target.PeriodEntries = Target.PeriodEntries + 1
            END
        ELSE
            BEGIN
                RETURN 1
            END 
        RETURN 0
        END
    WHEN NOT MATCHED BY Target
    THEN
        BEGIN
            INSERT INTO Target (Email, PromoName, PeriodEntries, PeriodExpires) VALUES (@Email, @PromoName, 1, DATEADD(day, 1, GETDATE()))
            RETURN 0
        END

END

PS：每个BEGIN和END都有下划线，说法语不正确......