Comparing string values in field calculator

Question

I am trying to compare the values of 2 fields in my attribute table and update a 3rd field as a result. In the field calculator I have

CASE when (("Address") like ("COUNTYNAME" )) then 'Match'
else 'Error'
End 

so for the following toy data examples I would get the result Match,Error,Error Address,COUNTYNAME

• Smith, Smith County
• Bob, Smith County
• Jane, Bob County

I have also tried CASE when (("Address") IN ("COUNTYNAME" )) then

Are there any other ways to compare text values within QGIS?

Answer 1

You can do something like this to compare two fields together:

Case
When "Address" in (left( "CountyNM", strpos("CountyNM", ' ')-1)) Then 'Match'
Else 'Error'
End

The strpos() function will return the index position of the first ' ' (space) character and the left() function "trims" the string before that position. The -1 is to ensure that the space will not be included when doing comparison.

Here is the output of the above expression:

enter image description here

Answer 2

The correct syntax is :

CASE WHEN "Address" LIKE ('%' || COUNTYNAME|| '%') THEN 'Match' ELSE 'Error' END

for the LIKE fonction to work you need to concatenate (using '||' ) the '%' wildcard (replace 0 to n character) with your field name, also you could add some UPPER or LOWER to convert to all uppercase (or all lowercase) to avoid false negative

• Michael: Is that not comparing the value from Address with a stationary COUNTYNAME instead of comparing the values in row [x] of field Address with field COUNTYNAME
• J.R: This should compare the value of row(x) of the Address field with the value of row(x) of the COUNTYNAME field .
• J.R: There is no ' around COUNTYNAME so it's taken as a field name, if you want you could put " around the field name it will work the same...