SQL 101: String-Related Functions, Part 1 - Converting Almost Anything to a String

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SQL provides more, much more, than the aggregate functions discussed in the previous article. This time around, I'll start to explore the scalar functions.

 

There are many scalar functions, ranging from trig functions (yes, they do exist in SQL) to date- and time-handling functions. I'll start with a few scalar functions that allow you to convert almost anything to a string.

 

By definition, a scalar function takes input argument(s) and returns a single value result. A scalar function can be used wherever an expression can be used (for instance, the Select, Where, or Group By clauses of a Select statement).

 

The restrictions on the use of aggregate functions I discussed in the previous article do not apply to scalar functions, because a scalar function is applied to single parameter values rather than to sets of values. The argument of a scalar function can be another function. However, the restrictions that apply to the use of expressions and aggregate functions also apply when an expression or aggregate function is used within a scalar function.

 

There are a lot of scalar functions and IBM keeps adding more with each DB2 enhancement. My initial plan is to address a few of them, namely those related with string- and date-handling, but there are many more, purposely built to handle XML, DataLinks, math, trigonometry, and a lot more. I'll let you, dear reader, take the helm and suggest other types of functions to discuss in this series. Because you probably have no idea what SQL has to offer, it might be easier to explain a problem/situation and I'll try to find the best function or functions to solve it.

 

When I get stuck with a problem that I have no idea how to solve, I usually check out IBM's DB2 for i Reference manual for the complete list of SQL functions. I always find the solution (or at least, the inspiration) I need to tackle the issue at hand.

 

Because there are so many string-related scalar functions, let's divide them into more manageable subsets and address these one by one, starting with the string conversion-related functions. Of these, the ASCII function is certainly the easiest to grasp. It returns the ASCII code value of the leftmost character of the argument as an integer. I'll keep using the same InvMst table introduced in the second article of this series in most of my examples. For instance,

 

SELECT      ASCII(ItemID)

FROM        InvMst

WHERE       ItemID = 'A123'

GROUP BY    ItemID

 

returns 65, because that's the integer value for the ASCII representation of 'A'. SQL also provides a function to perform the inverse operation: CHR. I'll use a system dummy table named SYSDUMMY1 to illustrate the way it works:

 

SELECT            CHR(65)

FROM        SYSIBM.SYSDUMMY1

 

This statement returns 'A', because that's the ASCII representation that corresponds to the 65 integer value. You could go nuts here and do some function nesting; something like SELECT CHR(ASCII('A')) FROM SYSIBM.SYSDUMMY1 would return 'A', because the processing is performed from the inside out, which means that the database engine would evaluate ASCII('A'), return 65 and then would use that as input parameter for the CHR; this in turn would return 'A'. I know this is an idiotic and useless example of function nesting, but it's also a nice way to illustrate the function-nesting concept in SQL.

 

The CHAR function is very similar to RPG's %CHAR BIF: it takes a numeric expression as an input parameter and converts it to the respective string representation. If the expression to be converted is either a Decimal or Floating-point expression, you can specify a second parameterthe decimal separator. You can also use CHAR to convert date/time data types to their string representation; in this case, the second parameter is the format. The possible values are ISO, EUR, USA, and JIS. The table below details each of these possible values.

 

Accepted Formats for Date Conversion Using CHAR

Format Name

Abbreviation

Date Format

Example

International Standards Organization (*ISO)

ISO

'yyyy-mm-dd'

'2014-11-16'

IBM USA standard (*USA)

USA

'mm/dd/yyyy'

'11/16/2014'

IBM European standard (*EUR)

EUR

'dd.mm.yyyy'

'16.11.2014'

Japanese industrial standard Christian era (*JIS)

JIS

'yyyy-mm-dd'

'2014-11-16'

 

 

Here's an example of CHAR's possible use:

 

SELECT            ItemID

, CHAR(ItemQty)

            , CHAR(LotNbr)

            , CHAR(ExpDate, ISO)

FROM        InvMst

WHERE       ItemID = 'A123'

            AND WHID = 333

            AND ShelfID = 77

 

This will return the item quantity, lot number, and expiration date in string format. Note that I could have specified a second parameterthe decimal separator characterfor the item quantity (ItemQty is a DECIMAL(9,2) field) as I did for expiration date (ExpDate is a Date field; therefore, I specified the date format ISO), but I chose not to do it because the second parameter is optional.

 

The VARCHAR function provides similar functionality, but it returns a varying-length string instead of a "traditional" fixed-length string. Note that varying-length strings are mostly used with language C APIs. VARCHAR provides a nice and easy way of converting a fixed to a varying-length string. The following statement returns the item Id field as a varying-length string:

 

SELECT            VARCHAR(ItemID)

FROM        InvMst

WHERE       ItemID = 'A123'

GROUP BY    ItemID

 

It's also important to mention that both CHAR and VARCHAR can be used to convert numeric and character data to the respective string representation.

 

Even though it has a somewhat similar name, VARCHAR_FORMAT is very different from VARCHAR. While VARCHAR can be used to convert several data types, VARCHAR_FORMAT can be used only to convert the timestamp or timestamp-compatible data types to the respective string representation. But there's a twist: VARCHAR_FORMAT's second parameter is the format string to apply to the timestamp. In a way, this provides functionality similar to RPG's %EDITW BIF. Here's an example that returns the current data and time in a user defined format:

 

SELECT            VARCHAR_FORMAT(NOW(),'YYYY-MM-DD HH24:MI:SS')

FROM        SYSIBM.SYSDUMMY1

 

This statement returns the current date and time, formatted in a more "human readable" way. I chose a simple format, but there are quite a lot of them available. Here are a few examples:

 

  • 'HH24-MI-SS'
  • 'HH24-MI-SS-NNNNNN'
  • 'YYYY-MM-DD'
  • 'YYYY-MM-DD-HH24-MI-SS'
  • 'YYYY-MM-DD-HH24-MI-SS-NNNNNN'

 

You can build your own formatting string, using the symbols explained in the VARCHAR_FORMAT section of the DB2 for i Reference manual. There, you'll find a rather large table detailing all the different possibilities.

 

The next article will continue to discuss string-related functions, which you can use to perform lowercase to uppercase conversions, among other interesting things. Until then, feel free to use the comments section below to agree, disagree, suggest topics for coming articles, or share your knowledge and experience with other readers. I'll be looking forward to hearing from you!

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