在不首先轉換爲日期時間時性能顯着下降

Question

在查詢中，當我在查詢中使用字符串作爲日期時，我發現查詢中的性能下降（速度降低了2倍-3倍），而不是將字符串值放入首先變量爲smalldatetime。因此，例如，例如

declare @rptDate AS smalldatetime 
set @rtpDate = CAST('2014-06-22' AS smalldatetime) 
SELECT SUM(tons) FROM sales 
WHERE ItemClass IN (1, 3, 5, 7) 
    AND AcctNo LIKE '31_-30[12]0' 
    AND YEAR(InvDate) = YEAR(@rptDate) 
    AND MONTH(InvDate) = MONTH(@rptDate) ' 
    AND DAY(InvDate) <= DAY(@rptDate) 

肯定比

SELECT SUM(tons) FROM sales 
WHERE ItemClass IN (1, 3, 5, 7) 
    AND AcctNo LIKE '31_-30[12]0' 
    AND YEAR(InvDate) = YEAR('2014-06-22') 
    AND MONTH(InvDate) = MONTH('2014-06-22') 
    AND DAY(InvDate) <= DAY('2014-06-22') 

那麼，爲什麼 「適當的優化」 不是這裏發生的更快？

Answer 1

我會去一個進一步

declare @rptDate AS smalldatetime 
declare @year as int 
declare @month as int 
declare @day as int 
set @rtpDate = CAST('2014-06-22' AS smalldatetime) 
set @year = year(@rtpDate) 
set @month = month(@rtpDate) 
set @day = day(@rtpDate) 

SELECT SUM(tons) FROM sales 
WHERE ItemClass IN (1, 3, 5, 7) 
    AND AcctNo LIKE '31_-30[12]0' 
    AND YEAR(InvDate) = @year 
    AND MONTH(InvDate) = @month 
    AND DAY(InvDate) <= @day