SQL datediff

Reference:
http://www.dotblogs.com.tw/lastsecret/archive/2010/10/04/18097.aspx

1. 將文字轉為日期格式：CONVERT(datetime, TG003)
2. 今天的日期：GETDATE()
3. 天數差異：DATEDIFF(day, date_before, date_after)

Ex: 查詢超過七天未結案的進貨單
SELECT     TG001, TG002, TG003, TG021
FROM         dbo.PURTG
WHERE     (TG013 = 'N') AND (DATEDIFF(day, CONVERT(datetime, TG003), GETDATE()) > 7)