Today s Experts. Mastering Dates Using SEQUEL 1. Technical Consultant. Technical Consultant

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1 Today s Experts Steven Spieler Vivian Hall Technical Consultant Technical Consultant Mastering Dates Using SEQUEL 1

2 Mastering Dates Using SEQUEL Mastering Dates Using SEQUEL 2

3 Working with dates on the System i can be confusing. Confusing Dates I'm sure you have seen how challenging dates can be to work with on the System i. Different applications store dates in many ways. In one file you might see one format, and in another file the format is completely different. On some systems you may have dates that have been entered incorrectly or don t have a value yet. Maybe the date field contains a zero or is blank. In one file you may have character fields for dates, and in another file they are stored as a number. What you want is to be able to display your dates properly in interactive requests or in reports. You want to use dates to choose records and to sort output. You want to manipulate dates to solve business issues and answer questions. All of this can be a challenge. Mastering Dates Using SEQUEL 3

4 Understanding dates can help you answer your business questions. Learn about Dates Understanding dates is complicated for two reasons. First, you need to understand how dates might be stored and learn how to apply SEQUEL functions to convert and manipulate your dates. Secondly, and more importantly, you have to understand YOUR dates - where they are, what they are, and what they mean. Just as data can be different between applications, data will vary from business to business and from process to process. Understanding how your data is stored, how it is used, and how it relates to your organization is the key to solving any data issue. Mastering Dates Using SEQUEL 4

5 Many users are unaware of date issues and how to solve them. Character dates with different padding Numbers that may or may not be a real date Blanks or zero dates Dates stored in separate fields Different date formats and attributes Date Issues Issues related to dates are numerous and varied. Based on experience we have seen many common issues such as: Character dates with different padding (leading vs. trailing blanks). Numbers that may or may not be a real date. Blanks or zero date values. Dates stored in separate fields. Dates stored in different formats and with different attributes. How is record selection and sorting affected by these issues? How do I control how dates look? Again, understanding your data and how to use SEQUEL will help you solve any date related issue. Mastering Dates Using SEQUEL 5

6 SEQUEL helps solve your daterelated issues and questions. SEQUEL Can Help SEQUEL has many date related functions that will help you create, manipulate, and control your dates. Fields can be combined, or taken apart. You can control how to display your dates in views and reports. SEQUEL has functions to make your dates look like anything you want month-day-year, or year-month-day, and so on. There are functions that can help you test for valid date values and functions to help you work with, or work-around zero and blank values. You can perform date arithmetic, create durations, and much more. Mastering Dates Using SEQUEL 6

7 Learn these techniques and functions to control date issues. System i date-related issues and common problems How to use SEQUEL to create and manipulate dates Real-world examples Learn Techniques There are many resources available to help you learn about SEQUEL and date related functions. From webinars to on-site, instructor led training, to user guides and on-line help built into the software. All of these can help you expand your understanding of SEQUEL. Based on the volume of calls and requests from our users, we developed this session to address the many date issues we see in support. In the next hour we will discuss three areas related to dates: System i date related issues and common problems How to use SEQUEL to create and manipulate dates How to solve some common problems Mastering Dates Using SEQUEL 7

8 Understand How the System i Stores Dates Dates on the System i This first section of today s presentation will focus on three areas: We will spend some time talking about how dates can be stored on the System i and their different attributes. Next, we will look at issues related to dates that we see most often in support. I'm sure you will recognize many of these problems as well. Finally, we will talk about true dates on the System i Date Data Types. Mastering Dates Using SEQUEL 8

9 Historically, dates have been stored as character and numeric values. Characters and Numbers Before date data types were introduced most applications we have encountered used character and numeric fields to store date values. Date and time values are special kinds of information. Although they are referred to in numeric terms, they are constrained by rules that don t apply to base 10 numbers such as: Month values must be integers between one and twelve Day values must be integers greater than zero and less than 28, 30, or 31 February 29 is sometimes (but not usually) allowed The format and attributes for the data may have been dictated by the application, the decision of the developer, or sometimes storage was a factor. Remember Y2K? Sometimes you will see separate year, month, day and century fields that together represent a particular date for a given file or application. Mastering Dates Using SEQUEL 9

10 The System i can store date values in many formats. Form mmddyy mmddyyyy ddmmyy ddmmyyyy yymmdd cyymmdd yyyymmdd yyddd cyyddd yyyyddd Example Date Formats As the table shows above, date values come in many shapes and sizes. Some are better than others depending on what you are trying to use them for. Some may be better suited for display purposes. Some may make sorting output easier than others. Some lend themselves to record selection better than others. Numeric fields make arithmetic manipulation easier than character fields. Character fields can be manipulated as well but require an extra step to convert them to number. Mastering Dates Using SEQUEL 10

11 Dates can be stored in separate fields. Separate Fields Many databases will have dates separated into several fields. There can be fields for the month, day, and year values. A common fix for Y2K field size issues was to add a separate century field to a file. So you might see a separate century and date field that when combined will produce the full date with a 4 digit year. In the past, we could use math to combine these fields together if they were numeric. Mastering Dates Using SEQUEL 11

12 Users see many common issues when it comes to dates. Presentation, sorting, and record selection Data mapping and select/omit errors Creating prompts for dates Common Issues As we have seen, dates can be stored with different attributes, in different formats, and even in separate fields. It is no wonder users have encountered so many issues related to dates. The most common issues we have seen are: Zeros and blank dates can make presentation confusing and present problems with sorting and record selection. Data mapping errors and select-omit errors. What do they mean and what causes them? Many people want to make data requests easier for users by prompting for input. Dates for prompts and the correct syntax can cause confusion. Mastering Dates Using SEQUEL 12

13 Dates stored as zero or invalid dates. How to display? How to work around? How to convert? Zero Dates Dates that are stored as numeric or character can sometimes be zero or blank. If a package hasn t been delivered, or a patient hasn t checked out of the hospital, or an outstanding receivable hasn t been collected, these dates will be blank or zero. This is not necessarily a bad thing. It just presents a different set of issues to be aware of. How do you want to display a zero date in your views or reports? Do you want to set them to a default value? Do you simply want to skip them altogether during record selection? Invalid Dates Invalid dates are values that aren't real like December 32 nd, or a month of 13. This usually represents erroneous data in the file. Using SEQUEL, you can test for them, and decide what to do with them. Either change them, skip them, or fix them in the file. Mastering Dates Using SEQUEL 13

14 Data mapping and select/omit errors when converting. Error Messages Another issue seen by our users has to do with date related error messages. Depending on your choices for working with bad or zero values you may encounter error messages returned by the query processor. Data mapping errors occur when you attempt to convert a character or numeric field containing a bad or zero value to a date. This typically happens when CVTDATE is used on the SELECT clause Select / Omit errors happen most often when you attempt to use a converted date containing bad or zero dates for record selection. Typically, this occurs when CVTDATE is used on the WHERE clause. Mastering Dates Using SEQUEL 14

15 Using dates as a prompt value. Date Prompts A third issue we receive many calls about has to do with date prompts. Prompts can easily be added to views for all data values. However, date data fields or converted dates require some special consideration if you want to prompt for them in your views. We will look at how to solve all three of these issues in the third part of this presentation. Mastering Dates Using SEQUEL 15

16 More and more databases are storing dates as date data types. Date Types Date types are a relatively new data format on the System i. We will see the power and versatility of this unique format and how to take advantage of it using SEQUEL. Mastering Dates Using SEQUEL 16

17 Date data type fields are intelligent. Intelligence Date data type fields are considered intelligent in that they are seen by the System i as a true date. Because of this, they can be manipulated in many ways. They can be added and subtracted to and from each other to create new date values. They can be compared against each other for record selection and used to sort data correctly regardless of how the date values are displayed. Unique Date data type fields are neither character nor numeric. They are a unique type of data. A benefit of this is they can never be zero, and should never be invalid. Mastering Dates Using SEQUEL 17

18 Date types can be manipulated in many ways. Date Manipulation The power of date data types lies in the ability to manipulate and use them in different ways. They can be added together and subtracted from each other to create new date values. Durations can be created easily and individual date elements (month, day, year) can be extracted. Mastering Dates Using SEQUEL 18

19 How to Work With, Convert, and Manipulate Dates Working with Dates We will now spend some time talking about different ways to work with date fields, including true date types, system values, and dates converted from your numeric or character values. Mastering Dates Using SEQUEL 19

20 Use CVTDATE to create true dates from your char and number fields. Form mmddyy mmddyyyy ddmmyy ddmmyyyy yymmdd cyymmdd yyyymmdd yyddd cyyddd yyyyddd Example Format MDY MDY1 DMY DMY1 YMD CYMD YMD1 JUL CJUL JUL1 CVTDATE If your date values are not stored as date data types but you know how they are formatted in your database, then you can convert them into date data types in your view. Once converted you gain all the advantages of date data types. SEQUEL includes a date conversion function that makes it easy to convert dates in your System i database into date data type fields. CVTDATE can convert any of 10 different formats into date type values. The table above can be found in the Sequel Quick Reference card, the user guide and the on-line help. You can see an example of a date value, it s form and format. The format is used in the CVTDATE function. Mastering Dates Using SEQUEL 20

21 CVTDATE syntax and examples. CVTDATE(field, fmt) Syntax There are only two forms for the CVTDATE function. One for a single field, and one for separate date fields. The example above shows the syntax for a single field. You only need to specify the field name and the format separated with a comma. The CVTDATE function will accept almost any valid numeric or character date provided that its length and format matches one of the allowed types. This is where knowledge of your database is important. Is the date you want to convert Y-M-D, or M-D-Y, or is it a Julian date? Is it an 8 position field or 6? Mastering Dates Using SEQUEL 21

22 Use CVTDATE with separate fields. CVTDATE(cc, yy, mm, dd) Syntax This second example shows the syntax for separate date fields. There is no format to specify. Just make sure to put the fields in the order you see here (high to low), and separate them with commas. Mastering Dates Using SEQUEL 22

23 Extracting individual elements from date type fields. Date/Timestamp/Duration YEAR(expression) MONTH(expression) DAY(expression) DAYOFWEEK(expression) DAYOFYEAR(expression) QUARTER(expression) WEEK(expression) returns the year (4,0) returns the month (2,0) returns the day (2,0) returns value 1-7 with Sunday as 1 returns value returns value 1-4 returns value 1-53 Extract Functions Many functions are available to extract just a portion of a date, time, or timestamp expression. These functions can be used on date fields, a literal value, or an expression. Mastering Dates Using SEQUEL 23

24 Using system values. External Values Several reserved fields can be accessed within your SEQUEL statement to acquire information about the current operating system environment. The external values can be used in any part of the SEQUEL statement that date/time/timestamp values or literals can appear. So, you can add them to the SELECT for display, or in an expression, or you can use them in the WHERE for record selection. These fields return current System i system values for date, time, timestamp and timezone. The data type and length of the returned values match the data type implied by the name. The external values is accessed one time. Each row of the query will have the same value. Mastering Dates Using SEQUEL 24

25 CURRENT DATE WHERE duedate < CURRENT DATE SELECT DAYS(CURRENT DATE) DAYS(orderdate) WHERE YEAR(CURRENT DATE) = YEAR(paydate) Current Date You will use CURRENT DATE in many ways in your views. For record selection you can perform age-based filtering as in the first example. You can use the DAYS function to calculate the number of days between two dates. In the last example, we can filter records to show only payments made in the current year. Mastering Dates Using SEQUEL 25

26 Perform date math with date fields. Subtract to create date durations Increment to create new dates Decrement to create new dates Date Math There are three arithmetic operations allowed using date and time values: subtraction, increment and decrement. Mastering Dates Using SEQUEL 26

27 Subtract dates from each other to create durations. Date Date = Date Duration Time Time = Time Duration Timestamp Timestamp = Timestamp Duration CVTDATE( , ymd1) 5/1/2007 = 10,424 Subtraction Date subtraction is the simplest date operation. The result is a date duration - the number or years, months and days between the two dates. Sometimes the result of a date subtraction can be confusing. This is because the result looks like any other (8,0) decimal value, but it has special meaning because it represents elapsed time. The result of the example above - 10,424 - tells us there is 1 year, 4 months and 24 days between the two dates. Mastering Dates Using SEQUEL 27

28 Add or subtract date values to create a new date. Date + Date Duration = Date Value Time + Time Duration = Time Value Timestamp + Any Duration = Timestamp Value Date Date Duration = Date Value Time Time Duration = Time Value Timestamp Any Duration = Timestamp Value Increment / Decrement Date/time arithmetic also allows a date/time/timestamp value to be incremented or decremented by a duration. The result is a value of the same data type that has been changed by some interval. Adding or subtracting a number of months from a date has the same effect as turning pages on a calendar. The day portion of the result is unchanged unless doing so would cause an invalid date (such as September 31) in which case it is adjusted to reflect the end of the month Mastering Dates Using SEQUEL 28

29 Increment / Decrement Examples SELECT * FROM custmast WHERE CURRENT DATE 30 Days > paydate SELECT * FROM ordhead WHERE CVTDATE(cooyr,coomn,coody) + 1 month < CURRENT DATE SELECT oidate + 30 years COLHDG( Maturity date ) FROM security SELECT cname, paydate, paydate + 2 MONTHS + 27 DAYS FROM custmast Examples The first three examples above use a duration to increment or decrement a date value. The resulting date value can be presented to the user or used in a comparison with another date. Increment or decrement expressions requiring complex durations with a number of years, months and days can also be created. The last example demonstrates an increment for both months and days in the same statement. The increment uses a complex labeled duration of 2 months and 27 days. Mastering Dates Using SEQUEL 29

30 Use Date Data Types to Solve Common Problems Solve Date Issues In this final section of today s presentation, we will spend some time and see how to apply what we have learned about working with dates to solve some common date related issues. We will look at different ways to handle dates in your files that may be zero or invalid. There are many functions that we can use to set them to a default, present them, or skip them. We will look at different ways to create aging, and use this to create conditional columns for type results. Lastly, we will see how dates need some special consideration when filtering records and when using run-time prompts in the WHERE clause. Mastering Dates Using SEQUEL 30

31 Problem Solved: Working with zero and invalid dates. Zero or Blank Dates We know that using CVTDATE on a zero or invalid date will generate some errors in our view. We will see some ways to work around this issue. Invalid Dates We will use CASE in conjunction with the VALID_DATE function to test the validity of the date value. Mastering Dates Using SEQUEL 31

32 Use CASE to work with your zero dates. Zero Dates We could use the GREATEST function to process a default date value in place of a zero. CASE is used more often to conditionally test for a zero and then use a default value. If your derived column is for display only, you can use the CHAR function to cast the value to whatever date form you like. In the results above we use the USA format to display the date with slashes and a 4 digit year. If you want to display and sort on the converted date field, you can use NULL as the default value. Mastering Dates Using SEQUEL 32

33 Use the VALID_DATE function to test your values. 1=True 0=False -1=Invalid Length -2=Invalid Type Valid Date Function The VALID_DATE function will evaluate a date value and a date type and return an integer result of 1 if true, 0 if false, -1 if the length is invalid, and -2 if the type is invalid. Using these results we can test our date field and then convert it when it is valid. CASE makes this very easy to do as in the example above. Mastering Dates Using SEQUEL 33

34 Valid Date Syntax: VALID_DATE(value, type ) Form mmddyy mmddyyyy ddmmyy ddmmyyyy yymmdd cyymmdd yyyymmdd yyddd cyyddd yyyyddd Example Type *MDY *USA *DMY *DMY *YMD *CYMD *YMD *JUL *JUL *JUL Valid Date Syntax The VALID_DATE syntax is very simple. Specify a date value and a type. The incoming date value can be character or numeric. The function can test many different formats. In the chart above, you can see an example of a date value, it s form and the type value required by the VALID_DATE function. Notice the type must be enclosed in quotes. Mastering Dates Using SEQUEL 34

35 Problem Solved: Aging and date difference. Aging One of the most popular requests we receive in support is how to do aging type operation. There are many ways to create the results shown above. Long ago you would create separate work files for each of the summary columns and join them together in a final view. The conditional calculations in the report writer will also work well for this kind of request, but the results can t be output to an Excel file. This view uses CASE and a DAYs duration to create the aging columns. Mastering Dates Using SEQUEL 35

36 Calculate Days difference. DAYS(paydte) DAYS(idate) = Days Difference DAYS Using the DAYS function on a date value, as in the DAYS(paydte) expression above, will convert the date to a number of days between that date and the start of the System Calendar. When the days of the invoice date is then subtracted, we end up with a number of days between the two dates. Each column will conditionally display the invoice amount field if the days difference falls within the range specified. Mastering Dates Using SEQUEL 36

37 Problem solved: Record selection and date fields. Date Filtering As you can see the value you use to test against a date field requires quotes. The system recognizes this value and automatically converts it to a date type. This is why date prompts can be tricky to set up in your view. Mastering Dates Using SEQUEL 37

38 Use the proper syntax. idate BETWEEN &&BEGDATE AND &&ENDDATE idate BETWEEN 6/1/2008 AND 10/1/2008 Date Prompt Syntax Prompting for date values is different than any other type of prompt. You need to create your prompt as usual in the WHERE clause, but with a slight difference in the syntax. What we see in the example above is WHERE the invoice date is between a beginning date variable and an ending date variable. Both are surrounded in quotes. Notice for dates we need to use two ampersands instead of the usual single ampersand. The value that is tested against the date field will end up looking like a character string month, day, and year, separated with slashes and surrounded in quotes. This is why we use quotes around the variable, and because we use quotes, we must use two ampersands to designate a variable in the SQL. Mastering Dates Using SEQUEL 38

39 In Conclusion: Dates can be confusing and cause many users difficulty. Once you understand your data, and master these techniques, you can gain control over date-related issues. Summary We saw how dates might be stored on the System i and the issues users face when trying to work with date values. We learned how to use Sequel s CVTDATE function to create, present, and manipulate dates and system values in our views. Lastly we solved some real-world problems encountered by many users on the System i such as: Zero and invalid dates Aging and date difference Record selection with date prompts Once you understand your data, and master these techniques, you can gain control over date related issues. Mastering Dates Using SEQUEL 39

40 We are ready for your questions! Today s Experts Steven Spieler Vivian Hall Technical Consultant Technical Consultant Mastering Dates Using SEQUEL 40

41 Thank you for joining us today! CONTACT INFORMATION: Web site: Telephone: or Handouts: Mastering Dates Using SEQUEL 41