Have you got a function similar to SQL NVL ?

I work with a group of people who are all experts in SQL. They all also have varying levels of technical skills and QlikView skills. One question I get frequently is whether QlikView has a function like the SQL NVL function.

For those of you not familiar with relational database SQL language, the NVL function takes two arguments: a field name or expression and a default value to be returned if the first argument is null. For example, a SQL database query may include the function like this:

  NVL(ORD_DISCOUNT, 0) AS ORD_DISCOUNT

And that would tell the SQL processor to look at the value of ORD_DISCOUNT and if it is null then return 0 as the function value otherwise return ORD_DISCOUNT.

When people ask about achieving the same thing with QlikView, I usually start by telling them that they can code an “if” statement like this:

  If(IsNull(ORD_DISCOUNT), 0, ORD_DISCOUNT)

and then I explain that there is a built-in QlikView function that can be used similar to NVL as long as the field you are checking is supposed to be numeric. It is the Alt function.

The Alt function accepts any number of arguments and looks at each of them going from left to right and returns whichever one is a valid number. So, repeating our example, if ORD_DISCOUNT is null then the following function will return a zero but if ORD_DISCOUNT is a valid number then the function returns ORD_DISCOUNT:

  Alt(ORD_DISCOUNT, 0)   

The Alt function will treat the last or rightmost argument as an “else” condition and return that value if none of the preceding arguments are numeric. The rightmost value need not be numeric so you could code something like this:

  Alt(ORD_DISCOUNT, 'Discount is missing')

The Alt function may be used in the loadscript code or in chart expressions.

If you are interested, the QlikView Help (search in Help for Conditional Functions) shows an interesting example for how the Alt function can be used to identify a date when the date value may be any one of several different date formats.  

  ★★★

Testing the Aggr Function Used in an Expression

I’m often asked to take a look at someone's QlikView document with the explanation that “the expression doesn't work”. If it is a complex expression with multiple parts or multiple functions I suggest taking each part of the expression and testing it to make sure it is performing the expected function. When one of the parts is something simple like  sum(InvoiceAmt)  then most people get the idea that they can put that little part of the expression into a temporary chart column or text box and then, based on the current selections and/or chart dimension, check that the function is really showing the sum of the invoice amounts.

If the part of the expression that needs to be tested is an aggr function then you need to know how to check it because the aggr function does not return a single value like the sum function; it returns an array of one or more values. An array of multiple values will usually show up as a null in a chart expression or text expression. If the array happens to have only one value or if all of the values in the array are exactly the same then you will be able to see the result of the expression but its no guarantee that the function is working as intended.

In order to test the aggr function itself, I recommend surrounding the aggr function with a concat expression that will help you analyze the array of the values returned by aggr. For example, if you had a straight table chart with a dimension of geographic region, you might have an expression like this to calculate average sales rep invoice amount totals:
  Avg( Aggr( sum(InvoiceAmt), SalesRep) )

In order to view the values returned by the aggr function, you could create a temporary column and copy and paste the aggr portion of the original expression and surround it with a concat function that might look like this:
  Concat( Aggr( sum(invoiceamt), SalesRep), ' / ' )

That would create a text string showing the individual values in the array separated or delimited by ' / '
Another useful delimiter is ', ' which creates a text string showing the individual values separated by commas.

When using this technique with a chart column there might not be enough space to show all of the array values separated by the delimiter. If that happens, right-click on the chart cell you would like to examine and choose Copy to Clipboard - Cell Value (in a text box you may right-click and choose Copy to Clipboard - Text) and then paste the value into a text file or spreadsheet or other convenient place to review a long text string.

If the array of values you see using this method is what you expected then check out all of the other sections of your expression – if all of them are working as you expect then assembling them into a single expression should work in your application. I often recommend building and testing each of the parts as a development technique when building a complex expression.

One other method for examining the array of values returned by the aggr function is to use it in a temporary chart and use the aggr function as a calculated dimension. A calculated dimension is, by definition, an array of values and it may help you review the values. 

_______________ ___________________ ___________________

Note to Santhosh:   You can remove leading zeros from a numeric identifier like a SAP 18-digit material number in the loadscript with a line like this:
   replace(ltrim(replace(MATNR,'0',' ')),' ','0') as MATNR_NO_ZEROS,

If you foresee the need to do a left join load using the original identifier then keep it as a separate field. If you would like to turn this into a user-defined function like I wrote about three years ago (search on "qlikview maven user-defined function") then do this:

1. Create a variable named DropZeros
2. Paste this into the variable:  replace(ltrim(replace($1,'0',' ')),' ','0')
3. Now, you have something that works like a user-defined function. It could be used in your loadscript line like this:

   $(DropZeros(MATNR)) as MATNR_NO_ZEROS,

★★★

Blinking Text Box

Occasionally, I’m asked if QlikView supports blinking text. Here’s a method that you can use if it is necessary. I don’t recommend this technique unless you have some kind of seldom used message that the document user absolutely must see (like “This data is invalid” or “Warning. Your chair is on fire!”) In any case, it is easy to try it out and see what the effect looks like.

Text in a text expression can be made to blink between two alternate forms with something like this:

=if(Odd(Second(Now(1))), '*** Hey, Look ***', '/// *** \\\')

Something more effective at attracting attention is to blink the background color of a text box.  Your text box should show constant text or a text expression that does not use the Now() function. And, the background color expression could be made to blink between two colors like this:

=if(Odd(Second(Now(1))),Cyan(),Yellow())

Expressions like these could be used to “blink” any of the document properties that can be controlled with an expression. The Now function in these expressions does use up some of your computer’s CPU time. A single expression is negligible but if you had several of these expressions using the Now function it could consume more than a few percent of your CPU capacity.


[The fish x-ray pictures in this blog posting and the one last week make great iPad wallpaper images]

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List Box to Select Values From Two Fields at Once

I posted this answer on QlikCommunity yesterday and several people remarked on it so I thought I’d repeat it here.

I recently had a QlikView document that showed lagged sales forecast data. There were two date fields used in the data: a Create_Date indicating when the sales forecast was created, and, a Fcst_Date indicating which week was being forecasted. For example, a forecast of sales for the week of June 21st might be created two weeks earlier on June 7th. Then the Create_Date would be 07JUN2012 and the Fcst_Date would be 21JUN2012.

In the document, in addition to other list boxes and a multibox, I added a list box that allows a user to view and select values from both date fields at the same time.
I created a new List Box and in the Properties General tab, I didn’t select a field, instead I chose <expression> and typed this into the expression:
='Create date=' & Create_Date & ' and ' & 'forecasted week=' & Fcst_Date
I made the title of the list box “Select Create and Forecasted Dates”.
Now, I had a list box that showed the pairs of dates that occur in the data. The values in the list box can be green when they are selected or white when they are possible values and gray when they are excluded values just like any other list box. When I click on a value in the list box it selects the corresponding values from each of the two date fields at the same time.

One additional refinement was to make the values sort the way I want them. I opened the Properties of the list box and chose the Sort tab and checked the Expression box and then in the expression box I typed just the field name, Create_Date

This idea would work with any pair (or trio) of fields where being able to view the field values together and select the values together makes sense.


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QlikView Tutorial

People often come across this blog when they are searching the web for information about how to use QlikView. If you have a working copy of QlikView on your computer then you already have links to excellent information. Start up the QlikView application and look at the start page -- click Resources and you should see something like the picture on the left. Those links will take you to current information about QlikView. There's a lot of basic info but it isn't just for beginners - I never fail to find something new and useful in the QlikTech and QlikCommunity websites.

If you don't have a working copy of QlikView or can't find the start page then follow this link: Click here for QlikView Information

or follow this link to the QlikCommunity: Click here for QlikCommunity