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Important SQL server functions - date functions

2022-07-28 04:24:00 【Navicat China】

The first 3 part ： Date function

stay IT I'm working in the industry 20 Years later, , I can determine the date and time, which is very difficult to deal with . Fortunately, , Modern relational databases （ for example SQL Server） There are many very useful functions for this . In today's article , We will explore some of the most commonly used functions .

Get the current date and time

Every programming language needs a way to get the current date and / Or the method of time . stay SQL Server in , There are two ways to do this CURRENT_TIMESTAMP and GETDATE() Function to get the current date and time . Both use “YYYY-MM-DD hh:mm:ss.mmm” Format returns the current date and time ：

that , Why use these two functions ？ As you can see in the screenshot above ,GETDATE() Need brackets , and CURRENT_TIMESTAMP You don't need brackets . This makes it very suitable for setting the default value of the audit field , For example, the creation date and last modification date columns ：

DATEPART

Being able to get the current date and time is one thing , But sometimes you need to parse each date part . This is it. DATEPART（） The use of functions . It returns the specified part of the date as an integer value . This is its grammar ：

DATEPART(interval, date)

interval（ interval ） The parameter must be a specific date part or abbreviation . for example , Year can be expressed as year、yyyy or 、yy . This is the complete list ：

year, yyyy, yy = year
quarter, qq, q = season
month, mm, m = month
dayofyear, dy, y = One day of the year
day, dd, d = One day of the month
week, ww, wk = Zhou
weekday, dw, w = On weekdays
hour, hh = Hours
minute, mi, n = branch
second, ss, s = second
millisecond, ms = millisecond

The following query divides the current date into days 、 Month and year components ：

DATEFROMPARTS

Date or time functions can also help us build dates based on different data . It accepts years 、 Month and day as input parameters , And combine them to form a complete date ：

DATEFROMPARTS(year, month, day)

Here is an example ：

DATEADD

Adding a date or time interval to a date or subtracting a date or time interval from a date is the most common date operation . stay SQL Server in , The function to do this is DATEADD. It accepts three input parameters ： Interval to add , Quantity and the date to which the interval is applied ：

DATEADD(interval, number, date)

DATEADD The interval between acceptance and DATEPART At the same interval , We have said before , Therefore, I will not repeat . Instead, , Let's take a look at some examples of this important function .

Our first example adds three months to today's date ：

To subtract the interval , Just provide a negative parameter ：

DATEDIFF

Our last function returns the difference between two date values , Expressed in the interval provided （ See above , For a complete list of accepted values ）：

DATEDIFF(interval, date1, date2)

The following query returns the difference between two dates in months ：

The first date is usually regarded as the earlier date , therefore , If the second date parameter is before the first date , be DATEDIFF The result is expressed as a negative value ：

summary

In today's article , We introduced some of the most important SQL Server Date and time functions . In the next issue （ It's also the last issue ） in , We will study other functions . If you are right about Navicat for SQL Server Interested in , Free trial 14 God ！