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) is reached, 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; after 100 years have occurred, the measure is called a century. After 1000 years have occurred, the measure is called a millennium; but the decade, the century, and the millennium are hardly used in calculations).
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 support date values, the SQL provides a data type named DATETIME. It is equivalent to Microsoft Access Date/Time data type.
As stated already, every language or system provides some standard formats for date values. You can indicate the format a new field should use or you can change the format of an existing field.
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 user 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.
The StatesStatistics database should still be opened.
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.
Microsoft Access provides two techniques to assist the user in specifying the value of a date-based field. To make data entry easy, after you have specified the data type of a field as Date/Time or Date & Time, in both the table and the form, the field or text box becomes equiped with a calendar. The calendar appears on the right side of the field or the text box when the object receives focus. The user can then click the calendar and select the desired date. The calendar completely reduces the likelihood of a mistake.
As an alternative to the calendar, the user can manually type the value of the date. In this case, the user must respect the rules of both the format that was set and the language that is being used. This means that the value to enter depends on the format that was set, if any. The value also depends on the universal rules of date. For example, the month of January cannot have more than 31 days and the month of February can have 29 days only if the specified year is leap.
If no format was set, after entering the value, the user can press Enter or Tab. At this time, Microsoft Access would analyze the value the user entered. If the value is not valid, Microsoft Access would display an error and reject the value. This is one of the fundamental differences between a text-based field and a date-oriented column. In a text-based field, the user can enter any date, including one that is not valid. You would find out only when you try to use that value in an operation.
Before involving a value or an expression in a date-based operation, you should first convert it. If the values of a table field are provided as strings, the primary way to convert them is to change the data type of the column to a date-based type. If all values are valid, the conversion would be smooth. If at least one of the values is not valid, the conversion would fail and you would receive an error.
This function takes a value, an expression, or the name of a field as argument and analyze it. The value of the argument must follow the rules of dates specified by both the universal conventions and the language being used (such as US English). If the argument holds a valid date, the function returns that date. If the value is not valid, the function returns an error.
We saw that a date was made of the day, the month, and the year. On an existing date, you can get these values by calling their corresponding functions.
This function takes a date as argument. If the argument is a valid date, the function produces the year as a number.
In most operations that involve date values, you will consider that the first day of the week is Sunday, represented with 1. In some cases, if you want to use another day as the starting point of a week, you can specify it from one of the above values.
This function takes three arguments with only the first required. The first argument is passed as an integer and can be one of the above values. The second argument is optional and it specifies whether the weekday name will be abbreviated. The third argument, firstdayofweek, also optional, specifies what day should be considered as the first day of the week. It can be one of the above numbers.
The first argument is required. It can be an expression or a control that must produce a date. If the function succeeds, it produces a number that represents the day of the week.
To let you know the current date on a computer, Microsoft Access provides a function named Date.
The date1 and date2 arguments are required. They specify the date values for the operation.
By default, the days of a week are counted starting on Sunday. If you want to start counting from another day, pass the option1 argument using one of the following values: 1, 2, 3, 4, 5, 6, or 7 (there are other variances to that argument).
If your calculation involves weeks, or if you are trying to find the number of weeks, by default, the weeks are counted starting January 1st. If you want to count your weeks starting at a different date, use the option2 argument to specify where the program should start.
The StoreItems form should still be opened in Design View.
The number argument is required. It specifies the number of units you want to add or subtract. If you set it as positive, its value will be added. If you want to subtract, pass it as a negative value.
A time is a non-spatial measure of the number of seconds that have elapsed in a set period. Starting at a specified period and counting incrementally, if the number of seconds reaches 60, the measure is called a minute. If the number of minutes reaches 60, the measure is called an hour. If 24 measures of hours occur, the measure is called a day (actually a day is 24 hours plus a few more seconds but the seconds are taken into consideration only every 4 years).
The SQL support time values with the same DATETIME data type used for dates.
This also represents a time in the morning. Remember that you can also include the seconds in your time value.
To support time values, Microsoft Access uses the same Date data type reviewed for dates. If you are creating a field in a table, to make it hold time values, if you are working in the Datasheet View, apply the Date & Time type as we reviewed for the date. If you are working in the Design View of the table, specify the data type of the field as Date/Time.
The Format property in the Design View of a table 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, click Input Mask and type a mask. Otherwise, you can click the ellipsis button and follow the wizard.
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.
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 give you the current time, Microsoft Access provides a function named Time.
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 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.
Required also, the Time1 and Time2 arguments specify the time values that will be used when performing the operation.
In some cases, you may want to consider both the date and the time as one value. Microsoft Access supports this concept through the same Date/Time data type we have seen so far. In fact, when you set the data type of a field to Date & Time or Date/Time and set the format for a date, you are simply asking Microsoft Access to ignore the time part; otherwise, the time becomes set to midnight.
The SQL DATETIME data type is used for dates, times, or combinations of date and time values.
A date/time value is a combination of the date and the time. If you want a Date/Time based field to hold both the date and the time values as one, you can set its Format as Long Date. An alternative is to create a mask that is a combination of the dates and the times masks we reviewed in previous sections.
When a field or a text box that is used for both the date and the time value is accessed, if you know the date and time combination you want to use, type it between # symbols. An example would be #06/15/2016 10:44. Otherwise, when the field or the text box has focus, it displays a calendar button on the right side. You can use it to specify the value of the date. You should then press the Space bar and type the time value. The field or the text box would then display both values.
To get both the current date and the current time of the computer, call a function named Now.
Because the date/time value is a combination of date and time, it includes the components we reviewed for the date and those we reviewed for the time. As a result, you can call their functions to get the individual values.
To add a value to date and time value, you can call the same DateAdd() function used for date or time values. This allows you to add months, days, years, hours, minutes, or seconds. The result would include both the date and the time.
If you provide only date values to a the DateDiff() function, you will get only the raw days, months, or years. In the same way, a call to the DateDiff() function is suitable only if both times occur on the same day. As a better alternative, the Date data type (actually called a class) allows more precision if you provide a combination of the date and time values for each part.
In the text box, click <<interval>> to select it and type "n"
Click the Recommendations tab and, in the text box, type The whole tune was completed.