[英]how to compare two dates in same column in SQL
我必须比较它们在表格的一列中的两个日期,我需要这个比较来找到我需要的特定日期之前和之后的日期,我还必须在 3 个不同的列中显示它们
我写了这段代码,但它完全错误:
CREATE VIEW
AS
SELECT (CASE
WHEN T1.BuyDate > T2.BuyDate THEN T1.BuyDate END)
AS PreviousBuyDate, T1.ItemName, T1.BuyDate,
(CASE
WHEN T1.BuyDate > T2.BuyDate THEN T1.BuyDate END)
AS NextDate
FROM FoodSara_tbl T1 , FoodSara_tbl T2
GO
输入:
|ItemName | BuyDate | ItemOrigin |
|---------|---------|------------|
| cake |2020-10-2| UK |
| coca |2020-5-2 | US |
| cake |2019-10-6| UK |
| coca |2020-12-2| US |
Output:
|PreviousDate | ItemName | BuyDate |NextDate |
|-------------|----------|---------|---------|
| NULL |cake |2019-10-6|2020-10-2|
| NULL |coca |2020-5-2 |2020-12-2|
|2019-10-6 |cake |2020-10-2| NULL |
| 2020-5-2 |coca |2020-12-2| NULL |
PS:我必须安排好日期。
用LAG
function 试试这个:
select LAG(BuyDate,1) OVER (PARTITION BY ItemName ORDER BY BuyDate asc) previous_date
, ItemName
, BuyDate
, LAG(BuyDate,1) OVER (PARTITION BY ItemName ORDER BY BuyDate desc) next_date
from FoodSara_tbl
查看最终结果: sqlfiddle
或者
使用LAG
和LEAD
function:
select LAG(BuyDate,1) OVER (PARTITION BY ItemName order by BuyDate) previous_date
, ItemName
, BuyDate
, LEAD(BuyDate,1) OVER (PARTITION BY ItemName order by BuyDate) next_date
from FoodSara_tbl
查看最终结果; sqlfiddle
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