跪求，这条话语为什么不能用

跪求，这条语句为什么不能用

SQL code

-- 用完整的产品列表填充该TABLE变量INSERT INTO @ProductSELECT ROW_NUMBER() OVER (ORDER BY Product.Id),       Id, Nick,NumIid, TrackIiid,ContactPhone,CategoryId,CreateTime,ModifiedTime,Sorting,EffectiveIntegral,ShareIntegralFROM ProductWHERE Id > 0IF @Category > 0AND CategoryId = @Category IF @Key <> ''AND Nick = @Key ORDER BY Id DESC

SQL code

DECLARE @sql varchar(max)SET @sql='SELECT ROW_NUMBER() OVER (ORDER BY Product.Id),       Id, Nick,NumIid, TrackIiid,ContactPhone,CategoryId,CreateTime,ModifiedTime,Sorting,EffectiveIntegral,ShareIntegralFROM ProductWHERE Id > 0 'IF @Category > 0BEGIN    SET @sql=@sql+' AND CategoryId = @Category 'ENDIF @Key <> ''BEGIN    SET @sql=@sql+' AND Nick = @Key 'ENDSET @sql=@sql+' ORDER BY Id DESC ' EXEC @sql