SQL 服务器 mm/dd/yy 或 yy/dd/mm 或其他格式的 T-SQL 日期数据类型格式？

Question

I am using this version of SQL Server

Microsoft SQL Server 2019 (RTM-GDR) (KB4517790) - 15.0.2070.41 (X64)   Oct 28 2019 19:56:59   Copyright (C) 2019 Microsoft Corporation  Developer Edition (64-bit) on Windows 10 Pro 10.0 <X64> (Build 19041: ) (Hypervisor) 

information about locale setting

select @@LANGUAGE;
-- result: us_english

I read reference document

(source: https://learn.microsoft.com/en-us/sql/t-sql/data-types/date-transact-sql?view=sql-server-ver15 )

I have

DECLARE @date DATE = '12/10/05';
DECLARE @datetime DATETIME = @date;

SELECT @date AS '@date', @datetime AS '@datetime';

As reference document point out, I think it is mm/[yy]yy/dd ( 12/10/05 ; December 5th, 1910), but it return December 10th, 2005 .

Is reference document wrong? How to easy-to-understand these format? How to understand and remember?

Answer 1

First thing is first - None of the Date/Time data types is stored with the display format in SQL Server.
Second, you've executed select @@LANGUAGE; and got back us_english - go on and run

SELECT dateformat 
FROM sys.syslanguages
WHERE [Name] = @@LANGUAGE;

And you'll see the result of mdy - which means that the formats for string representations of date values is one of the following:

• [m]m/dd/[yy]yy
• [m]m-dd-[yy]yy
• [m]m.dd.[yy]yy

Third, you should be aware of the fact that when dealing with SQL Server, the language settings are related to the default language of the login, which means different logins might have different language seetings, and of course, it is possible to change the language and / or the date format settings - which leads to the conclusion -

You should never rely on language settings for date/time string representations. Instead, use one of formats specified in ISO 8601 , since these are the only two formats guaranteed to be interpreted correctly to a valid date/time value, regardless of the language and dateformat settings, and regardless of the actual data type, Even DateTime And that's juse One reason why you should never use DateTime again ).