Using the field calculator to copy one column's values to another's BLANK values

Question

This is probably a basic and simple question which has been answered multiple times before, but my Google-fu has come up empty, so here we are.

Long story short, to simplify my analysis, I want to copy the data from the first zoning column field to the second into ONLY in cell values which are blank. I will attach a screenshot to show what I am talking about.

I have tried various [case when] and [if] examples, but nothing seems to get this thing to go.

enter image description here

Answer 1

Starting with a layer, in which some values in a field are blank, enter the following in Field Calculator and select Update Existing Field, zone_2:

if("zone_2" is null, "zone_1", "zone_2")

Alternatively, if the fields are simply blank rather than NULL, enter the following:

if( "zone_2" = '', "zone_1", "zone_2")

The result is the same, as shown below.

Before:

table prior to update, with nulls

After:

enter image description here

Answer 2

If your conditionnal test doesn't work you can also select the "right" features and update only those selected (there should be a checkbox to limit the changes) ...

• Benjamin Smith: UPDATE: Thanks. Yeah, I pretty much did this. I did a select by expression, then at the top of the attribute table I selected [overlay] and put in "zonedist" and clicked update selected. If someone wants to show how to do this with the field calculator though, I am all for learning new things :)