Database Date and Time Values

Practical Learning: Introducing Time Values

1. Start Microsoft Access
2. To create a new database, click File Name and type Georgetown Dry Cleaning Services
3. Click Create
4. Right-click the Table1 tab and click Design View
5. Set the name to Cleaning Orders and press Enter
6. Replace ID with CleaningOrderID
7. Click the empty box under CleaningOrderID and create the following fields:
    

   Field Name	Data Type	Field Size	Format	Default Value
   CleaningOrderID
   Customer Name		50
   Customer Phone		20
   Unit Price Shirts	Number	Double	Fixed	1.25
   Quantity Shirts	Number	Integer		0
   Unit Price Pants	Number	Double	Fixed	1.95
   Quantity Pants	Number	Integer		0
   Other Item1		50		None
   Unit Price Item1	Number	Double	Fixed	0.00
   Quantity Item1	Number	Integer		0

8. In the top section of the table, set the Data Type of the Other Item1 field to Lookup Wizard...
9. In the first page of the wizard, click the second radio button: I will type in the values that I want
10. Click Next
11. In the second page of the wizard, click the first empty field under Col1
12. Create the following items
     

    None

    Tie

    Coat

    Dress

    Other

    Jacket

    Swede

    Silk Shirt

    Sweater

    Comforter

    Women Suit

    Regular Skirt

    Men's Suit 2Pc

    Men's Suit 3Pc

    Skirt With Hook

13. Click Next
14. Accept the column label as Other Item1 and click Finish
15. Click the box on the left side of Other Item1
16. Press and hold Shift
17. Click the box on the left side of Quantity Item1
18. Press Ctrl + C to copy
19. Click the first empty box under Quantity Item1
20. Press Ctrl + V to paste
21. Change the field names to Other Item2, Unit Price Other2, and Quantity Item2 respectively
22. Click the first empty box under Quantity Item2
23. Press Ctrl + V to paste
24. Change the new field names to Other Item3, Unit Price Other3, and Quantity Item3 respectively
25. Click the first empty box under Quantity Item3
26. Press Ctrl + V to paste
27. Change the field names to Other Item4, Unit Price Other4, and Quantity Item4 respectively
28. Click the first empty box under Quantity Item4 and create the following two fields:
     

    Field Name	Data Type	Field Size	Format	Default Value
    Tax Rate	Number	Double	Percent	0.0775
    Notes	Memo

29. Right-click the Notes field and click Insert Rows
30. Set the name of the new field to Order Status and set its Data Type to Lookup Wizard
31. In the first page of the wizard, click the second radio button: I will type in the values that I want
32. Click Next
33. In the second page of the wizard, click the first empty field under Col1
34. Create the following items
     

    Not Ready

    Ready

    Picked Up

35. Click Next
36. Accept the column label and click Finish
37. In the lower section of the table, set its Field Size to 20
38. Set the Default Value to "Not Ready"
39. Save the table
     
    
40. To change the view, on the Ribbon, click the Datasheet View button

By default, to display or handle time values in a database, Microsoft Access uses some letters and characters. The default rules are defined in the Regional and Language Settings of Control Panel:

To support time values, Microsoft Access uses a data type named Date. Actually, if you are creating a field in a table, to support a time value, you use a category of data type called Date/Time. You can specify the type in the Datasheet View or in the Design View of a table.

To create a time-based field in the Datasheet View of a table:

• Click Click to Add and select Date & Time from the list
• Click the cell under Click to Add. On the Ribbon, click Fields. In the Add & Delete section of the Ribbon, click Date & Time

If you are creating the table in Design View, to configure a field that can hold time values, specify its Data Type as Date/Time:

In the Datasheet View, you can create a field that shows time values in a standard format. In the Datasheet View, to create a field that holds one of the time formats set in the Control Panel, click under Click to Add. On the Ribbon, click Fields. In the Add & Delete section, click More Fields and click either the Time am/pm, the Medium Time, or the Time 24hour option:

Practical Learning: Applying the Time Type to a Field

1. On the table, click the cell under Customer Phone
2. On the Ribbon, click Fields
3. In the Add & Delete section, click Date & Time
4. Type Time Deposited and press Enter
5. On the table, click the cell under Order Status
6. On the Ribbon, click Fields
7. In the Add & Delete section, click More Fields and click Medium Time
8. Type Time Picked Up as the name of the new field and press Enter
9. To switch the view, right-click the tab and click Design View
10. In the top section of the table, right-click Unit Price Shirts and click Insert Rows
11. Type Time Ready as the name of the new column
12. Set its Data Type to Date/Time

Microsoft Access allows you to customize how the time values would appear on the field. After creating a field, in the Datasheet View, click a cell under the column header. On the Ribbon, click Fields. In the Formatting section, select the desired option in the Format combo box as Long Time, Medium, or Short Time:

In the Design View, in the top section, click the name of the Date/Time field. In the lower section, click Format and select the desired option among Long Time, Medium, and Short Time:

As you can see, the Format property in the Design View provides two columns of information. The left column shows the names of time formats. The right column shows a preview of each option.

Practical Learning: Applying Time Formats

1. While the Time Ready field is still selected in the top section, in the lower section of the table, click Format and click the arrow of its combo box. Select Short Time
2. To change the view of the table, in the lower-right section of Microsoft Access, click the Datasheet View button
3. When asked to save the table, click Yes
4. On the table, click Time Deposited
5. On the Ribbon, click Fields
6.  In the Formatting section, click the arrow of the Format combo box and select Short Time

The Format property in the Design View is used to show how the time values should appear in the field. First, the user must enter the value. To assist the user with how to enter the time, you can create a custom mask. To do this, you can click Input Mask and type a mask. Otherwise, you can click the ellipsis button and follow the wizard.

As stated already, the rules that specify what characters and symbols are used to display time values are in the Time tab of the Customize Regional Options. The characters used for the hours, the minutes, and the seconds are defined in the Time Format combo box:

To control how time values should display in a field, after setting its Data Type to Date/Time, use the Format property. The characters used to create a format are:

When combining these characters to create a format, you should follow the rules of your language. You should refer to the formula set in the Time property page of the Regional (and Language) Settings of Control Panel. Microsoft Access also refers to it for the character separator. If you want to include any other character, type it in double-quotes.

To create a time value, you use an appropriate combination of the above letters and characters. In most cases, you should include the combination between two # signs. An example would be:

#05:42#

This would represent 5:42 AM. Another example is:

#10:26 AM#

This also represents a time in the morning. Remember that you can also include the seconds in your time value.

Operations on Time Values

There are two main ways you start with a time value. You can provide it to an object or you can get it from your database. If you are providing it, you can use the rules and combinations we reviewed above. On the other hand, if a time value already exists in your database, you can retrieve and use it as you see fit. In most cases, the users know how to specify a time value. In some cases, when getting a time, it may not be in a correct or recognizable format. Normally, before involving a value in a time-based operation, you should first check and convert it to a recognizable format. To support this, you can called a function called CDate. Its syntax is:

CDate(Expression) As Time

This function takes one argument that can be passed as the name of a control, as a string that holds a time value, or as an expression that is supposed to produce a time value. If the value passed as argument holds a recognizable time, the function returns that time.

As mentioned in our introduction, a time value is made of the hours, the minutes, and the seconds. If you already have a time or if you retrieve one from an object or you get one from an expression, you may be interested in only one or its components. There are functions you can use to get these values.

To get the hour value of a time, you can call the Hour() function. Its syntax is:

Hour(Expression) As Integer

To get the minute value of a time, you can call the Minute() function. Its syntax is:

Minute(Expression) As Integer

To get the second value of a time, you can call the Second() function. Its syntax is:

Second(Expression) As Integer

Each of these functions takes an argument that can be an expression that should produce a time value. The argument can also be the name of a control that holds a time value. The function then examines the argument and produces a number that represents the hour, the minute, or the second respectively.

Microsoft Access provides various functions to perform date and time related operations. These functions allow you to add times, find the difference between time values, or add constant values to time values.

To give you the current time, Microsoft Access provides a function called Time.

Practical Learning: Getting the Current Time

1. To change the view of the table, in the lower-right section of Microsoft Access, click the Design View button
2. In the top section, click Time Deposited
3. In the lower section, click Default Value and type =Time()

One of the operations you can perform on a time consists of adding a value to it. To support this, you can use the DateAdd() function. To find a backward time, you can use the DateDiff() function.

The DateAdd() function is used to add an interval time value to a specific time. With it, you can add a number of seconds, minutes, or hours to another time. The syntax of the DateAdd() function is

DateAdd(Interval, Number, date) As Time

The Interval argument is required and it specifies the kind of value you want to add. This argument is passed as a string, thus enclosed between double quotes and can have one of the following values:

The Number argument is required also. It specifies the number of units you want to add. If you set it as positive, its value will be added. If you want to subtract, make it negative.

The date argument is the date to which you want to add the number.

The DateDiff() function is used to find the difference between two time values. It allows you to find the number of seconds, minutes, or hours when you supply two recognizable values. The DateDiff() function takes 5 arguments, 3 are required and 2 are optional.

The syntax of the function is

DateDiff(Interval, Time1, Time2, Option1, Option2) As Time

The Interval argument is required and it specifies the kind of value you want to subtract. This argument is passed as a string and can have one of the following values:

Required also, the Time1 and Time2 arguments specify the time values that will be used when performing the operation.

Fundamentals of Dates

A date is a non-spatial measure of the number of days that have occurred in a period. When a certain number of days, namely 28, 29, 30, or 31 (depending on some factors), the measure is called a month. When 12 months have occurred, the measure is called a year (after 10 years have occurred, the measure is called a decade but the decade is not used in calculations; after 100 years have occurred, the measure is called a century but the century is not used in calculations; after 1000 years have occurred, the measure is called a millennium but the millennium is not used in calculations).

By default, to display date values in a database, Microsoft Access uses some letters and characters. As mentioned for times, the rules for dates are built in the operating system and you can check them in the Regional and Language Settings of Control Panel:

As reviewed for the time, to support date values, Microsoft Access internally uses a data type named Date. In a table, this data type is referred to as Date/Time. Over all, dates and times are considered differently but, to specify that a field would use date, time, or both, set its Data Type to Date/Time. You can specify this data type for a field what creating a table either in the Datasheet View or in the Design View.

To create a field that receives or displays date values, in the Datasheet View of a table:

• Click Click to Add and select Date & Time from the list
• Click the cell under Click to Add. On the Ribbon, click Fields. In the Add & Delete section of the Ribbon, click Date & Time

If you are creating the table in Design View, to configure a field that can use date values, specify its Data Type as Date/Time.

As stated already, the Control Panel provides some standard formats for date values. To create a field that uses one of them, while a table is displaying in the Datasheet View, click under Click to Add. On the Ribbon, click Fields. In the Add & Delete section, click More Fields. In the Date and Time section, click either Short Date, Medium Date or Long Date.

Practical Learning: Applying a Date Type

1. In the top section of the table, right-click Time Deposited and click Insert Rows
2. Type Date Deposited as the name of the new field
3. Set its Data Type to Date/Time
4. To change the view, right-click the Cleaning Orders tab and click Datasheet View
5. When asked to save the table, click Yes
6. On the Table, click under Time Deposited
7. On the Ribbon, click Fields
8. In the Add & Delete section, click Date & Time
9. Type Date Ready as the name of the new field and press Enter

After a valid date value has been entered in a field, you can specify how the date would display, not necessarily how the date was entered:

• If you are working in the Datasheet View, after creating a Date/Time field, click a cell under that column header. On the Ribbon, click Fields. In the Formatting section, select the desired option in the Format combo box as General Date, Long Date, or Short Date
• If you are working in the Design View, in the top section, click the name of the field. In the lower part, click the Format combo box and select General Date, Long Date, Medium Date, or Short Date

Those are the most popular formats used for dates. If none of those satisfies you, you can use the following characters or symbols to create a desired format:

To use these letters, simply type the desired combination in the Format field. Here is an example:

This is configured to display a single digit for a day of the month if the day is less than 10, followed by the complete name of the month, followed by the year in 4 digits.

During data entry, the data entry person can enter a valid date. Once the field looses focus, it displays the date based on the format. Based on this, you can use any combination of formats but you should use a combination most regularly used in your language so the users would not be confused.

Besides the indicated characters, you may want to use some other characters to separate them. An example would be January 5, 2004, which uses a comma in the display. To create such sections, include the characters in double-quotes. What you would be doing is to ask Microsoft Access to display such characters "as is" while considering the non-quotes characters as part of the format. Here is an example:

Practical Learning: Applying a Date Format

1. On the table, click Date Deposited
2. On the Ribbon, click Fields
3. In the Formatting section, click the arrow of the Format combo box and select Long Date
4. To change the view, right-click the Cleaning Orders tab and click Design View
5. In the top section, right-click Time Picked Up and click Insert Rows
6. Set its name to Date Picked Up and set its Data Type to Date/Time
7. In the lower section, click the arrow of the Format combo box and select Long Date

In the Design View of a table, the Format property allows you to specify how a date would display in a field but not how the user must enter it. To specify how the date must be typed in a field or control, you can use the Input Mask property. You can either type the mask or you can click the ellipsis button and follow the wizard. If you want to type your mask, you can use an appropriate combination of the letters and symbols we saw above.

Year(Expression) As Integer

Month(Expression) As Integer

WeekdayName(weekday As Integer,
	    Option As Boolean,
	    Optional firstdayofweek As Integer) As String

Weekday(Expression, Optional firstdayofweek As Integer) as Integer

DateAdd(Interval, Number, date) As Date

DateDiff(Interval, Date1, Date2, Option1, Option2)