問題描述

我正在閱讀前任編寫的腳本.

I was going through a script written by a predecessor.

誰能給我解釋一下為什么會有這個說法

Can someone explain to me why would this statement

--- CreatedDateTime is a datetime column in SALES_ORDER table.
SELECT * FROM SALES_ORDER
WHERE GETDATE() - CreatedDateTime < 1

返回與

SELECT * FROM SALES_ORDER 
WHERE DateDiff(hh,CreatedDateTime, GetDate()) < 24

推薦答案

從 DATETIME 中減去 數(shù)字 記錄在 此處:還可以從日期中減去一個數(shù)字，以天為單位."

Subtraction of a number from a DATETIME is documented here: "Can also subtract a number, in days, from a date."

declare @Now as DateTime = GetDate();
declare @OneWeekAgo as SQL_Variant = @Now - 7;

select @Now as [Now], @OneWeekAgo as [Delta], SQL_Variant_Property( @OneWeekAgo, 'BaseType' ) as [Data Type];

在使用帶有日期和時間數(shù)據(jù)的運(yùn)算符類型:要對所有日期和時間數(shù)據(jù)類型進(jìn)行加減運(yùn)算，請使用 DATEADD 和 DATEDIFF."

Under Using Operators with Date and Time Data Types: "To add and subtract for all date and time data types, use DATEADD and DATEDIFF."

在可能違反最小驚訝原則的情況下，我們看到了以下奇怪的結(jié)果:

In a possible violation of the Principle of Least Astonishment we see the following curious result:

declare @Now as DateTime = GetDate();
declare @Then as DateTime = '17760704';
declare @Delta as SQL_Variant = @Now - @Then;

select @Now as [Now], @Then as [Then], @Delta as [Delta],
  SQL_Variant_Property( @Delta, 'BaseType' ) as [Data Type],
  Cast( @Delta as Int ) as [Days];

<小時>

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這篇關(guān)于t-sql中兩個日期相減的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！