sql - 获取当年的总计 - SQL

Question

我需要在访问数据库中使用 SQL 获取今年旅行的总里程数。目前我正在尝试以下查询，但它不起作用：

   SELECT 
      SUM(Mileage) 
   FROM 
      [Mileage-Expenses] 
   WHERE 
      YEAR(DatePurchased) = YEAR(CURRENT_TIMESTAMP)

任何想法如何解决这一问题？

Answer 1

A WHERE clause based on YEAR(DatePurchased) requires the db engine evaluate that expression for every row in the table. You would get better performance by adding an index on DatePurchased, if you don't already have one, and then using a WHERE clause which allows the db engine to retrieve only the rows from the current year before computing SUM(Mileage).

SELECT
    SUM(Mileage)
FROM 
    [Mileage-Expenses]
WHERE
        DatePurchased >= DateSerial(Year(Date()), 1, 1)
    AND DatePurchased < DateSerial(Year(Date()) + 1, 1, 1)

Answer 2

我已经很久没有使用 MS Access 了，但据我记得它不支持CURRENT_TIMESTAMP，你需要使用DATE()orNOW()代替：

   SELECT 
      SUM(Mileage) 
   FROM 
      [Mileage-Expenses] 
   WHERE 
      YEAR(DatePurchased) = YEAR(DATE())

http://office.microsoft.com/en-gb/access-help/use-current-date-and-time-in-calculations-HP001098479.aspx