Besides the month calendar control, the date picker is another good candidate to display date values. It primarily follows the same rules as the month calendar.

When you sort records based on a column that uses the date data types, the SQL interpreter must be able to identify each date/time value. Fortunately, the database engine can validate each date value and reject those that are not valid.

As seen for the other data types, if you sort records based on a column that uses a date/time type and if the column has null values, the records with null values would show first. The values of a date/time field are sorted in chronological orders. Here is an example:

using System;
using System.Data;
using System.Drawing;
using System.Windows.Forms;
using System.Data.SqlClient;

public class Exercise : System.Windows.Forms.Form
{
    Button btnSort;
    Button btnCreateTable;
    DataGridView dgvIceCream;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        btnCreateTable = new Button();
        btnCreateTable.Text = "Create Table";
        btnCreateTable.Location = new Point(12, 12);
        btnCreateTable.Width = 100;
        btnCreateTable.Click += new EventHandler(btnCreateTableClick);

        btnSort = new Button();
        btnSort.Text = "Sort";
        btnSort.Location = new Point(120, 12);
        btnSort.Click += new EventHandler(btnSortClick);

        dgvIceCream = new DataGridView();
        dgvIceCream.Location = new Point(12, 46);

        Text = "Ice Cream Factory";
        Controls.Add(btnCreateTable);
        Controls.Add(btnSort);
        Controls.Add(dgvIceCream);

        StartPosition = FormStartPosition.CenterScreen;
        dgvIceCream.Width = this.Width - 30;
        dgvIceCream.Height = this.Height - 80;
        dgvIceCream.Anchor = AnchorStyles.Left | AnchorStyles.Top |
                             AnchorStyles.Right | AnchorStyles.Bottom;
    }

    void btnCreateTableClick(object sender, EventArgs e)
    {
        using (SqlConnection cntIceCream =
                new SqlConnection("Data Source=(local);" +
                                  "Integrated Security='SSPI';"))
        {
            SqlCommand cmdIceCream =
                    new SqlCommand("CREATE DATABASE IceCreamFactory;",
                        cntIceCream);

            cntIceCream.Open();
            cmdIceCream.ExecuteNonQuery();

            MessageBox.Show("A database named IceCreamFactory has been created.",
                            "Ice Cream Factory",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
        }

        using (SqlConnection cntIceCream =
                new SqlConnection("Data Source=(local);" +
                                  "Database='IceCreamFactory';" +
                                  "Integrated Security=yes;"))
        {
            SqlCommand cmdIceCream =
                new SqlCommand("CREATE SCHEMA IceCream;",
                                cntIceCream);

            cntIceCream.Open();
            cmdIceCream.ExecuteNonQuery();

            MessageBox.Show("A schema named IceCream has been created",
                   "Ice Cream Factory",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
        }

        using (SqlConnection cntIceCream =
                new SqlConnection("Data Source=(local);" +
                                  "Database='IceCreamFactory';" +
                                  "Integrated Security=yes;"))
        {
            SqlCommand cmdIceCream =
                new SqlCommand("CREATE TABLE IceCream.Orders1" +
                               "(" +
                               "    OrderID int identity(1, 1) not null, " +
                               "    OrderDate date not null, OrderTime time null " +
                               ") " +
                               "INSERT IceCream.Orders1(OrderDate, OrderTime) " +
                               "VALUES(N'2011-02-14', N'10:12'), (N'2011-02-15', N'09:08'), " +
                               "      (N'2011-05-10', N'15:24'), (N'2011-07-04', N'14:01'), " +
                               "      (N'2011-04-18', N'19:16'), (N'2011-04-18', N'09:15'), " +
                               "      (N'2011-04-18', N'12:48'), (N'2011-07-04', N'11:26')",
                                cntIceCream);

            cntIceCream.Open();
            cmdIceCream.ExecuteNonQuery();

            MessageBox.Show("A table named Orders has been created in the IceCream schema",
                   "Ice Cream Factory",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
        }
    }

    void btnSortClick(object sender, EventArgs e)
    {
        using (SqlConnection cntIceCream =
                new SqlConnection("Data Source=(local);" +
                                  "Database='IceCreamFactory';" +
                                  "Integrated Security=yes;"))
        {
            SqlCommand cmdIceCream =
                new SqlCommand("SELECT OrderID, OrderDate FROM IceCream.Orders1 " +
                               "ORDER BY OrderDate;",
                                cntIceCream);
            SqlDataAdapter sdaIceCream = new SqlDataAdapter();
            DataSet dsIceCream = new DataSet("IceCreamSet");

            cntIceCream.Open();

            sdaIceCream.SelectCommand = cmdIceCream;
            sdaIceCream.Fill(dsIceCream);

            dgvIceCream.DataSource = dsIceCream.Tables[0];
        }
    }
}

public class Program
{
    [STAThread]
    static int Main()
    {
        System.Windows.Forms.Application.Run(new Exercise());
        return 0;
    }
}

This would produce

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:

• When the equality comparison is performed on dates, the values must occur on the exact same day to get a true value. Otherwise, the result is false
• When the inequality comparison is performed on dates, the values must occur on different days, which would produce true
• When the comparison for lower (or greater) value is performed on two date values, the first date must occur before (or after) the second for the comparison to produce a true value
• When the comparison for lower (or greater) or equal value is performed on two date values, the first date must occur either before (or after) the second date or both dates must occur on the same day. Such a comparison would produce a true value
• You can perform comparison for Not Greater Than operation, !>, on date values. This is the same as the Less Than Or Equal To operator "<="
• The comparison for Not Less Than, !<, operation is available on dates It is the same as >=

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))
GO

Like a string, the value of a date is provided or initialized in single-quotes. Unlike a string, the value of a date must follow strict rules inside the single-quotes, otherwise the value would be invalid. When performing comparisons on date-based fields, you must keep those rules in mind. Unlike strings but like numbers, date values support all Boolean operators.

Boolean operators used in date fields work as follows:

Here is an example:

SELECT StudentNumber, FirstName, LastName, DateOfBirth,
       Gender, City, SingleParentHome
FROM   Registration.Students
WHERE  DateOfBirth >= '1995-01-01';
GO

When it comes to comparisons, date values follow the same approach as numbers, but date values add some logical rules. To negate a date comparison, you can precede it with the NOT operator. If you negate an equality comparison, the expression would mean that the date doesn't occur on the indicated value, but it doesn't indicate whether the date occurs before or after that date. Therefore, in most cases, to negate a date comparison, you should use the opposite of the operator. Because date values support all Boolean operators, the opposites of those operators apply in the same logic we reviewed for numeric values:

As mentioned already, you have many options to use functions in your database. That is, Transact-SQL, the .NET Framework, and the Visual Basic library have many built-in functions you can use. You can also create your own functions in SQL or in a custom library (DLL).

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 create a date in the .NET Framework, you can use the following constructor of the DateTime structure:

public DateTime(int year, int month, int day);

To let you get the current date 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

To get the current date from the .NET Framework, the DateTime structure provides a property named Today:

public static DateTime Today { get; }

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))

To convert a string to a date value in the .NET Framework, the DateTime structure is equipped with the Parse() method that is overloaded with various versions.

Transact-SQL and the .NET Framework provide extensive support in the way a variable produces or a column displays the value of a date. In T-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.

To perform the same operation in the .NET Framework, the string data type is equipped with the Format() method that is overloaded with various versions. One of the versions uses the following syntax:

public static string Format(string format, Object value);

The first argument of this method is the same as the second argument of the Transact-SQL's FORMAT() function. The second argument is the same as the first argument of the FORMAT() function.

The days of months are numbered from 1 to 31, depending on the month. When way you can display the day is to use dd (lowercase). Here is an example:

DECLARE @DateValue DATE,
        @StrValue nvarchar(50);
SET @DateValue = N'20120604';
SET @StrValue = FORMAT(@DateValue, N'dd');
SELECT @DateValue AS Original;
SELECT @StrValue AS Formatted;
GO

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

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

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.

If you are passing an expression that should produce at least one more part such as the day, you can include M (uppercase). 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 display a month by its name using one of two formats: short (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, and Dec) or long name (January, February, March, April, May, June, July, August, September, October, November, or December).  To display the short name of a month, pass the format as MMM (uppercase).

The long names of months are . 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. 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. Whether passed by itself or in an expression that contains the other parts, yyy (lowercase) or yyyy (lowercase) produces a year in 4 digits.

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

Here is an example that produces a 4-digit year:

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

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

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.

To let you get the short date format, the DateTime structure is equipped with the ToShortDateString() method whose syntax is:

public string ToShortDateString();

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

D (uppercase) should not be used in a combination with letters for the month, the day, and the year.

To let you get the long date format, the DateTime structure is equipped with the ToLongDateString() method whose syntax is:

public string ToLongDateString();

Date addition consists of adding a number of days, a number of months, or a number of years, to a date value. The Transact-SQL 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

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

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

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

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:

DATENAME(integer ReturnedValue, date Value) RETURNS integer/nvarchar;

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 value. To let you get the day of a date value, the DateTime structure is equipped with the Day property:

public int Day { get; }

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

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 month of a date value, the DateTime structure is equipped with the Month property:

public int Month { get; }

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

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. To let you get the year of a date value, the DateTime structure is equipped with the Year property:

public int Year { get; }

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

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

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