Imagine that you have a report of sales data but there’s a defect in the data and some of the products don’t have a product description. You can’t make a selection on missing or null values in the product description field, named PROD_DESC for our example, but you can easily select the products that have a missing or null product description. Go to the listbox for the PRODUCT_ID field or click the pull-down arrow for PRODUCT_ID from a multibox. Now, start typing this expression:
You can use a slightly different expression to select products with a blank or null product description; type this instead =isnull(trim(PROD_DESC))
This technique is useful if you use QlikView to find data quality issues or to validate data from suppliers or customers.