Date Values
Date Values
Introduction to Date Values
Introduction
A date is a non-spatial value uses a combination of numbers, symbols, and strings (or names). As such, a date is made of various parts. The primary part of a date is called a day. A day can be considered as starting at sunset (when the sun appears) and ends at sundown (when the sun disappears). In reality, a day starts on a set point called midnight, which is in the middle of the night.
The day ends at the other middle of the night, the other midnight. Such a period (from one midnight to the other midnight) is used as a unit. It can be represented with a number or it can be given a name.
A series of 7 consecutive days is called a week. The days in a week can each be represented with a number (from 1 to 7) or with a name. A group of 28, 29, 30, or 31 consecutive days is called a month. The group is not random. It is strictly organized so that the month itself can be represented and in fact, the month has a name. Depending on its number of days, a month can have 4 or 5 weeks. In most simple situations, a month is considered to hafve 4 weeks.
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In some financial situations, a group of 360 consecutive days is called a year. In most calendars, a year can have 365 days every year except that, after 4 years, the year would have 366 days. This is referred to as a leap year. A group of 100 years is called a century. The years in a century can be identified with 2 digits. An example is 08. Another example is 78. One more example is 18. Normally, a year is represented with 4 digits, from 0 to 9999. A group of 1000 years is called a millennium. The years in a millennium must each be identified with 4 digits. An example is 1608. Another example is 1978. Yet another example is 2118. Within a year, each day can be identified by a numeric value. The number of days in a year depends on various factors. For example, in some scenarios, such as some commercial or accounting procedures, a year would count for 360 days. To help manage the days of a year, a year is divided in 12 consecutive units. Each unit is called a month. Each month can be identified by a number or a name. When a month is identified with a number, it can use a value between 1 and 12. When it comes to names, a month can use a long and/or a short name. The long names are January, February, March, April, May, June, July, August, September, October, November, and December. The short names are Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, and Dec. Each month has a certain number of days. A day in a month can be identified with an integer. The first day of the month is 1. The 15th day would be identified as 15 or Day 15. The number of days in a month depends on various factors. To help manage the months of a year, a year can be divided in either quarters or semesters. A year has 4 quarters that each contains 3 months. A year also has 2 semesters that each has 6 months. The combination of a day, month, and year is called a date.
To support dates, Transact-SQL provides the DATE data type. This data type counts dates starting from January 1st, 0001 up to December 31st, 9999. There are various rules you must follow to represent a date. The rules can be checked in the Date tab of the Customize Regional Options accessible from the Regional and Language Options of the Control Panel:
To initialize a DATE variable, use one of the following formulas: YYYYMMDD YYYY-MM-DD MM-DD-YY MM-DD-YYYY MM/DD/YY MM/DD/YYYY DD-MMM-YY DD-MMMM-YY DD-MMM-YYYY DD-MMMM-YYYY You can start the value with a 4-year digit. If you use the first formula, YYYYMMDD, you must provide 4 digits for the year, immediately followed by 2 digits for the month, immediately followed by 2 digits for the day. An example would be DECLARE @OneDay DATE;
SET @OneDay = N'10360610';
SELECT @OneDay AS [Day to Prevail];
GO
In US English, this represents October 6th, 1036:
You can provide the value in one unit with 6 digits. In this case, the left 2 digits would be considered the year in the current century. Instead of providing the whole value in one combination of digits, you can use the second formula, YYYY-MM-DD, which is the default date format in Microsoft SQL Server. Once again you must provide 4 digits for the year, followed by the "-" separator, followed by 1 or 2 digits for the month, followed by the "-" separator, followed by 1 or 2 digits for the day. An example would be DECLARE @EventDay date;
SET @EventDay = N'1914-4-7';
SELECT @EventDay AS [Event Day];
GO
This would produce:
If you are using a command prompt or PowerShell, make sure you include the value in single-quotes. To apply Unicode rules, start with the N prefix. Here is an example: 1> DECLARE @IndependenceDay DATETIME; 2> SET @IndependenceDay = N'01/01/1960'; 3> SELECT @IndependenceDay AS [Independence Day]; 4> GO Independence Day ----------------------- 1960-01-01 00:00:00.000 (1 rows affected) We saw that, if you use the MM-DD-YY or MM/DD/YY, you can provide a year with 2 digits. In this case:
If you are visually creating a column and you want it to use date values, select date in the Data Type combo box of the column:
To create a date-based column with SQL code, apply the DATE data type.
A date-based column uses various formulas for its values. Data entry depends on whether you are working visually or with SQL code. If you are working in a Table window, to specify the value of a DATE-based field, use one of the following formulas: MM-DD-YY MM-DD-YYYY MM/DD/YY MM/DD/YYYY DD-MMM-YY DD-MMMM-YY DD-MMM-YYYY DD-MMMM-YYYY YYYY-MM-DD If you are performing data entry programmatically, use one of the above formulas plus the following: YYYYMMDD
If you sort records from a column that uses a date-based data type, if the column has null sections, the records with null would show first. The values of a date field are sorted in chronological order. If the values use only date values, the records that occur first would come up first. If two records have the same value, the record that was created first would also come before the other.
Remember that Transact-SQL supports all types of logical operators to perform comparisons. These can be done of date values:
You can use any of the filter opeator we saw, such as BETWEEN or IN. You can also use conjunctions, disjunctions, and their combinations. You can also use a built-in function with any of the operators we know already. Here is an example: SELECT FirstName, LastName, Gender, DateOfBirth, SingleParentHome FROM Registration.Students WHERE (DateOfBirth BETWEEN TRY_CONVERT(date, N'1995-01-01', 102) AND TRY_CONVERT(date, N'1999-12-31', 102))
You have the option to create your own functions to use in a database. Still, Transact-SQL provides many built-in functions that you should first investigate before creating your own. You can involve a function in an operation, then use the result as the value to assign to a field. You can also call a function that takes one or more arguments; make sure you respect the rules of passing an argument to a function when calling it. You can also include a function in any of the operators we have reviewed so far. You can also involve a built-in function in an expression. To refine your data analysis, you can use functions, whether functions you create yourself or Transact-SQL built-in functions. As always mentioned, the first candidates of functions you should use are the built-in functions. To use a built-in function, in the placeholder of the column, type the name of the function, followed by its parentheses. If the function takes some parameters, remember to follow the rules to call a parameterized function.
We saw that there are so many ways to show a date value it can be confusing. In the same way, it can be confusing to compose a date. For example, what does 04-08-01 represents? It could be April 7, 2001. I could be August 4, 2001. I could be August 1st, 2004. To assist you with formulating a date by specifying a day, a month, and a year, Transact-SQL provides a function named DATEFROMPARTS. Its syntax is: DATE DATEFROMPARTS(int year, int month, int day) This function allows you to create a date if you have the year, the month, and the day.
To let you get the current date (and time) of the computer that a user is using, Transact-SQL provides a function named GETDATE. Its syntax is: GETDATE(); To get a date with more precision, call the SYSDATETIME function. Its syntax is: SYSDATETIME(); Imagine you have a database named AutoRepairShop and it has a table used to create repair orders for customers: CREATE TABLE RepairOrders ( ReceiptNumber int, CustomerName varchar(50), CustomerPhone varchar(20), RepairDate datetime2 ); GO When performing data entry for this table, you can let the user enter the customer name and phone number. On the other hand, you can assist the user by programmatically entering the current date. To do this, you would call the SYSDATETIME() or the GETDATE() function. Here are examples: INSERT INTO RepairOrders(ReceiptNumber, CustomerName, CustomerPhone, RepairDate)
VALUES(100001, N'Annette Berceau', N'301-988-4615', SYSDATETIME());
GO
INSERT INTO RepairOrders(ReceiptNumber, CustomerPhone, CustomerName, RepairDate)
VALUES(100002, N'(240) 601-3795', N'Paulino Santiago', SYSDATETIME());
GO
INSERT INTO RepairOrders(ReceiptNumber, CustomerName, RepairDate, CustomerPhone)
VALUES(100003, N'Alicia Katts', SYSDATETIME(), N'(301) 527-3095');
GO
INSERT INTO RepairOrders(ReceiptNumber, RepairDate, CustomerPhone, CustomerName)
VALUES(100004, SYSDATETIME(), N'703-927-4002', N'Bertrand Nguyen');
GO
As mentioned already, to let you convert a string to a date value, Transact-SQL provides the TRY_PARSE() and TRY_CONVERT() functions. These functions take a string as argument and they scan that argument. If it is a valid date, the function returns it. If not, the functions returns NULL. Here is an example: SELECT FirstName, LastName, Gender, DateOfBirth, SingleParentHome FROM Registration.Students WHERE (DateOfBirth BETWEEN TRY_CONVERT(date, N'1995-01-01', 102) AND TRY_CONVERT(date, N'1999-12-31', 102)) Formatting and Controlling the Display of Dates Introduction Transact-SQL and Microsoft Windows provide extensive support in the way a variable produces, or a column displays, the value of a date. In Transact-SQL, this is done using the the FORMAT() function. Its syntax is: FORMAT(value, nvarchar format [, culture ] ) RETURNS nvarchar This function takes two required arguments. The third is optional. If you are formatting a date, the first argument must have the original value. The second argument specifies how the formatting must be carried. A date value is made of one or many sections. If it contains many sections, they are separated by symbols, almost any, such as a period or a comma. In US English, the standard separators are / (forward slash) or - (dash). We will review the letters to use and their combinations.
The days of months are numbered from 1 to 31, depending on the month. One way you can display the day is to use dd (lowercase):
The names of the week use two formats: 3 letters or full name. To display a name with 3 letters, use "ddd" in the format argument. The names will be Sun, Mon, Tue, Wed, Thu, Fri, or Sat. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'ddd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
To display the complete name of a weekday, pass "dddd" by itself or include it in a complete format string. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'dddd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
To display the weekday and the numeric day of the month, you can create a format that combines both constants. When creating this string, the constants must be separated inside the string so the compiler would know which format to apply and where. To separate the formats, you can use (almost) any character but you should conform to those used in your regional settings. One of the most regularly used separators on dates is the comma but the simplest separator is an empty space. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'ddd dd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
Months are displayed using two categories: a number or a name. The months are numbered as follows: 1=January, 2=February, 3=March, 4=April, 5=May, 6=June, 7=July, 8=August, 9=September, 10=October, 11=November, and 12=December. To display only the number of the month, pass the format argument as MM (uppercase). In this case, the month is provided as an integer with 2 digits. If the number is between 1 and 9, it displays with a leading 0. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'MM');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
If you are passing an expression that should produce at least one more part such as the day, you can include M (uppercase). The difference becomes as follows:
Following the rules we applied to display a combination of a weekday and a month's numeric day, you can display a month and the month's numeric value. This time, instead of an empty space, you should use a character that would indicate that the date is displaying a combination of month and day (or day and month). The common character to use is the one that conforms to the regional settings of your computer. In the US English, this would be the forward slash "/". Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'M/dd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
In the same way you can combine a weekday (short or long name) followed by the combination of day/month (or month/day) as you see fit. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'ddd M/dd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
You can also use this format when constructing a combined date: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'dddd dd-MM');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
You can display a month by its name using one of two formats: short or long name. The short names of months are: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, and Dec. To display the short name of a month, pass the format as MMM (uppercase). You can pass MMM by itself to get just the short name of the month. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'MMM');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
As an alternative, you can include MMM in a combination that produces the other parts. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'dddd, dd-MMM');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
The long names of months are January, February, March, April, May, June, July, August, September, October, November, or December. To display the long name of a month, pass MMMM (uppercase) as the format. You can pass this constant as itself or along with the other parts. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'dddd, d MMMM');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
If you want to display the year in two digits, pass yy (lowercases) as the format. When used by itself, yy produces the year of the date argument. The year is provided with 2 digits. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20060604';
SET @StrValue = FORMAT(@DateValue, N'yy');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
In a combination with the day, the month, and the year, use yy to display the year with 2 digits. Examples are 06 or 14 or 68. We have already reviewed how the number is interpreted. Whether passed by itself or in an expression that contains the other parts, yyy (lowercase) or yyyy (lowercase) produces a year in 4 digits. From what we have seen so far, you can display a complete date using any format of your choice, such as the day, the month, and the year. Here is an example that shows the short weekday, the short name of the month, and the 2-digit year: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'ddd dd MMM yy');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
Here is an example the displays the long name of the day and the long name of the month: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'dddd d MMMM yy');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
A year value represented with two digits is hardly explicit, unless you have a good reason for using it. The alternative is to use all four digits to display a year. This format is created with the yyy (lowercase) or yyyy (lowercase). Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'yyy');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
Now we know how to create a short or a complete date value using the appropriate letters and the desired combination. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'dddd, MMMM dd, yyyy');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
You can pass the format as m or M. If you pass only m or M as the format, the function produces the long name of the month followed by the year in 2 digits. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20060604';
SET @StrValue = FORMAT(@DateValue, N'm');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
As an alternative, you can pass the format as y (lowercase) or Y (uppercase) only. In this case, the function would produce the full name of the month, followed by a comma, and the year in 4 digits: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20121004';
SET @StrValue = FORMAT(@DateValue, N'y');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
The standard way to display a date is called the short date format. It is defined in the Short Date section of the Date property page of the Customize Regional Options accessible from the Regional and Language Options of the Control Panel:
To display a date in the short date format, pass the second value as d (lowercase). In US English, the short date format is M/d/yyyy. The month is provided in digits. If the month and the day use a number from 1 to 9, it doesn't use a leading 0. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20060604';
SET @StrValue = FORMAT(@DateValue, N'd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
If d (lowercase) is used in a combination with letters for the month and year, the day is provided as 1 (for days from 1 to 9) or 2 (for days from 1 to 12) digits. An alternative is to pass G (uppercase) as the format argument:
Another alternative is to pass the format as g (lowercase):
Another common way to display a date is called the long date format. It is defined in the Long Date section of the Date property page of the Customize Regional Options. To display a date in the long date format, pass the second value as D (uppercase). In US English, the short date format is dddd, MMMM dd, yyyy. The weekday and the month are provided in full names. The day is provided with a leading 0 if its number is between 1 to 9. Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20060604';
SET @StrValue = FORMAT(@DateValue, N'D');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
D (uppercase) should not be used in a combination with letters for the month, the day, and the year. An alternative is to use f (lowercase). If f is passed by itself, the function produces the long date format followed by 12:00 AM Here is an example: DECLARE @DateValue DATE,
@StrValue nvarchar(50);
SET @DateValue = N'20060604';
SET @StrValue = FORMAT(@DateValue, N'f');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
This would produce:
The letter f should not be used along with the other letters and symbols. One more alternative is to pass F (uppercase) as argument:
Date addition consists of adding a number of days, a number of months, or a number of years, to a date value. The function used to perform this operation is DATEADD. Its syntax is: DATEADD(TypeOfValue, ValueToAdd, DateOrTimeReferenced) The first argument specifies the type of value that will be added. It can be one of the following values:
The second argument is the number of TypeOfValue to be added. It should be a constant integer. The third argument is the original value on which the operation will be performed. Here is an example that adds a number of years to a date value: DECLARE @Original date,
@Result date;
SET @Original = N'20121204';
SET @Result = DATEADD(yy, 2, @Original);
SELECT @Original [Original Date];
SELECT @Result [2 Years Later];
GO
This would produce:
Here is an example that adds 2 quarters to a date: DECLARE @Original date,
@Result date;
SET @Original = N'20121204';
SET @Result = DATEADD(Quarter, 2, @Original);
SELECT @Original [Original Date];
SELECT @Result [2 Years Later];
GO
This would produce
Here is an example that adds 5 months to a date: DECLARE @Original date,
@Result date;
SET @Original = N'20121004';
SET @Result = DATEADD(m, 5, @Original);
SELECT @Original [Original Date];
SELECT @Result [2 Years Later];
GO
This would produce
To find the difference between two dates, you can call the DATEDIFF() function. Its syntax is: DATEDIFF(TypeOfValue, StartDate, EndDate) The first argument specifies the type of value the function must produce. This argument uses the same value as those of the DATEADD() function. The second argument is the starting date. The third argument is the end date. Here is an example that calculates the number of years that an employee has been with the company: DECLARE @DateHired As date,
@CurrentDate As date;
SET @DateHired = N'2005/10/04';
SET @CurrentDate = N'20130622';
SELECT DATEDIFF(Year, @DateHired, @CurrentDate)
AS [Current Experience];
GO
This would produce:
Consider the following table: USE master
GO
IF EXISTS (
SELECT name
FROM sys.databases
WHERE name = N'PublicLibrary1'
)
DROP DATABASE PublicLibrary1
GO
CREATE DATABASE PublicLibrary1
GO
USE PublicLibrary1;
GO
CREATE SCHEMA Administration;
GO
CREATE TABLE Administration.Members
(
MemberNumber nchar(11),
FirstName nvarchar(25),
LastName nvarchar(25),
Gender int,
DateOfBirth date
);
GO
INSERT INTO Administration.Members
VALUES(N'93757-49411', N'Joshua', N'Ransome', 1, N'20020412');
GO
INSERT INTO Administration.Members(MemberNumber, FirstName, LastName, Gender)
VALUES(N'20304-70592', N'Chris', N'Drews', 3);
GO
INSERT INTO Administration.Members
VALUES(N'13594-60857', N'Ephraim', N'Chance', 1, N'19440824'),
(N'29283-47597', N'Jeannette', N'Gong', 2, N'19781104');
GO
INSERT INTO Administration.Members(MemberNumber, FirstName, LastName, DateOfBirth)
VALUES(N'39485-00741', N'Bobbie', N'Womack', N'19840602');
GO
INSERT INTO Administration.Members(MemberNumber, FirstName,
LastName, Gender, DateOfBirth)
VALUES(N'83758-30737', N'Mathilda', N'Bambeck', 2, N'19940816');
GO
Here is a list of the records: USE PublicLibrary1;
GO
SELECT mbrs.MemberNumber [Mbr #],
mbrs.FirstName [First Name],
mbrs.LastName [Last Name],
mbrs.Gender,
mbrs.DateOfBirth [Date of Birth],
DATEDIFF(Year, mbrs.DateOfBirth, SYSDATETIME()) Age
FROM Administration.Members mbrs;
GO
This would produce:
The immediate-if function, named IIF, is used to take action depending on the outcome of a condition. Its syntax is: IIF(Conditional Expression, What To Do If True, What To Do If False) RETURNS sql_variant; The IIF() function takes three arguments. The first is a conditional statement expressed using any of the logical operators we reviewed. The conditional statement is true, the function returns the second argument and stops. If the conditional statement is false, the function ignores the second argument and returns the third argument. Here are examples of calling the IIF() function: SELECT mbrs.MemberNumber [Mbr #],
mbrs.FirstName [First Name],
mbrs.LastName [Last Name],
mbrs.Gender,
mbrs.DateOfBirth [Date of Birth],
DATEDIFF(Year, mbrs.DateOfBirth, SYSDATETIME()) Age,
IIF(DATEDIFF(Year, DateOfBirth, SYSDATETIME()) <= 18, N'Teen', N'Adult') "Membership Category"
FROM Administration.Members mbrs;
GO
This would produce:
One way to expand the IIF() function is to nest one inside of another. To do that, you can replace one of the consequences (What To Do If True or What To Do If False) with an IIF() function. Here are examples: USE PublicLibrary1;
GO
SELECT mbrs.MemberNumber [Mbr #],
mbrs.FirstName [First Name],
mbrs.LastName [Last Name],
IIF(mbrs.Gender = 1, N'Male', IIF(mbrs.Gender = 2, N'Female', N'Unknown')) Gender,
mbrs.DateOfBirth [Date of Birth],
DATEDIFF(Year, mbrs.DateOfBirth, SYSDATETIME()) Age,
IIF(DATEDIFF(Year, DateOfBirth, SYSDATETIME()) <= 18,
N'Teen',
IIF(DATEDIFF(Year, DateOfBirth, SYSDATETIME()) <= 65,
N'Adult',
N'Senior')) "Membership Category"
FROM Administration.Members mbrs;
GO
This would produce:
Transact-SQL provides various options to get the day, the month, or the year of an existing date value. The values are gotten using some functions. One of the functions used is named DATENAME. Its syntax is: integer/nvarchar DATENAME(integer ReturnedValue, date Value); ReturnedValue specifies the value to get from the date. The second argument is the date that holds the value from which the value will be produced. The date value must be a valid date. If the date value is not valid, the function would produce an error. For example, 20110229 would return an error since the month of February in 2011 did not have 29 days. Besides DATENAME(), Transact-SQL provides the DATEPART() function. Its syntax is: DATEPART(int DatePart, date Value) The Value argument uses the same constants as for the DATENAME() function. The constants provided for ReturnedValue or Value are not case-sensitive. This means that year, YEAR, and Year would work the same. Transact-SQL provides additional functions to get the day, the month, and the year of a date.
A typical date combines a day, a month, and a year. The day is a numeric value within the month. To get the day in the month of a date value, you have various options. Transact-SQL provides the DAY() function whose syntax is: int DAY(date Value); This function takes a date as argument and produces its day. Here is an example: DECLARE @DateValue DATE,
@Result int;
SET @DateValue = N'20121004';
SET @Result = DAY(@DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
As an alternative, you can call the DATENAME() function and pass the ReturnedValue as Day (or day), d, or dd. Here is an example: DECLARE @DateValue DATE,
@Result int;
SET @DateValue = N'20121004';
SET @Result = DATENAME(dd, @DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
One more alternative is to call the DATEPART() function and pass Day (or day), d, or dd as the Value. Here is an example: DECLARE @DateValue DATE,
@StrValue int;
SET @DateValue = N'20120425';
SET @StrValue = DATEPART(Day, @DateValue);
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
In this case, both functions produce the same result.
A regular date contains a month. To get the numeric month of a date value, you have two options. You can use Transact-SQL's MONTH() function. Its syntax is: int MONTH(date Value); This function takes a date as argument and produces the month. Here is an example: DECLARE @DateValue DATE,
@Result int;
SET @DateValue = N'20121004';
SET @Result = MONTH(@DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
Notice that the MONTH() function returns an integer. Besides MONTH(), Transact-SQL provides the DATENAME() function. To get the month, pass the ReturnedValue as Month (or month), m, or mm. This means that you must consider the ReturnedValue as a string. Here is an example: DECLARE @DateValue DATE,
@Result nvarchar(30);
SET @DateValue = N'20121004';
SET @Result = DATENAME(mm, @DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
This would produce:
You can also use the DATEPART() function to get the month. In this case, you would pass the same argument as for the DATENAME() function.. Here is an example: DECLARE @DateValue DATE,
@StrValue int;
SET @DateValue = N'20120425';
SET @StrValue = DATEPART(Month, @DateValue);
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
To let you get the year of a date, Transact-SQL provides the YEAR() function. Its syntax is: int YEAR(date Value); Here is an example: DECLARE @DateValue DATE,
@Result int;
SET @DateValue = N'20121004';
SET @Result = YEAR(@DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
This would produce:
Another way to get the year value is to call the DATENAME() function. In this case, pass the ReturnedValue argument as Year (or year), yy or, yyyy. In this case, the function returns an integer. Here is an example: DECLARE @DateValue DATE,
@Result int;
SET @DateValue = N'20121004';
SET @Result = DATENAME(yy, @DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Formatted;
GO
In the same way, you can call the DATEPART() function to get the year. You would pass the argument as yy or yyyy, just as done for the DATENAME() function.. Here is an example: DECLARE @DateValue DATE,
@StrValue int;
SET @DateValue = N'20120425';
SET @StrValue = DATEPART(mm, @DateValue);
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO
The result is the same.
A year is made of four parts that each has 3 consecutive months. Each one of those parts is called a quarter. A quarter is represent with a small integer. The first quarter that contains January, February, and March has a value of 1. To get the quarter of a year of a date, you can call the DATENAME() or the DATEPART() function. In this case, pass the ReturnedValue or the Value argument as Quarter (or quarter), q or, qq. In both cases, the function returns an integer. Here is an example: DECLARE @DateValue DATE,
@Result nvarchar(30);
SET @DateValue = N'20120714';
SET @Result = DATENAME(q, @DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
This would produce:
A year is divided in 52 or 53 parts named weeks. Each week is made of 7 consecutive days. A week is represented as a small integer. To get the numeric week of a date, call either the DATENAME() or the DATEPART() function. Pass the ReturnedValue or the Value argument as week, wk or, ww. Here is an example: DECLARE @DateValue DATE,
@Result nvarchar(30);
SET @DateValue = N'20121231';
SET @Result = DATENAME(Week, @DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
This would produce:
As mentioned already, a week is made of 7 consecutive days and each or those days has a name.known as the weekday. To get the weekday of a date, call either the DATENAME() or the DATEPART() function. Pass the ReturnedValue or the Value argument as Weekday or dw. Here is an example: DECLARE @DateValue DATE,
@Result nvarchar(30);
SET @DateValue = N'20121231';
SET @Result = DATENAME(Weekday, @DateValue);
SELECT @DateValue AS Original;
SELECT @Result AS Result;
GO
This would produce:
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Practical
Learning: Introducing Date Values
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