How do I go about comparing two attributes from an update request?

I have the following in my default conf. file:

update request {
       SQL-Location := "%{sql: SELECT xxx}"
 }
      
update request {
       SQL-Location-Id := "%{sql: SELECT yyy }"
}

if (SQL-Location != SQL-Location-Id ) {
reject
}

And my debug log shows:

Info: Failed parsing "SQL-Location-Id": Unknown value SQL-Location-Id for attribute SQL-Location