Hi luoy,
Thanks for the reply. If I understand you correctly, you want me to create a custom field with checkbox type, so that I can then create a checkbox parametric search?
If so, I understand that this way I can get the functionality that I want. However, since the checkbox is only to check if another custom field has a value, this creates extra work for the client who will be inputting data – thus I was hoping this could be avoided.
I guess I could write a script to give a hidden custom field a value of "1" whenever a post is saved which has any value in the custom field of interest.
However overall I was hoping this could be avoided by View functionality. I think this could be easily implemented using IS NOT NULL SQL comparison operator. I.e. if the checkbox in the parametric search is left empty, then nothing is filtered; but if the checkbox is checked, then IS NOT NULL filter is applied to the specified custom field. Reversely, you could also add IS NULL to the available operators in View.