[feature request] Compare to other column

This repo is fantastic!

My application's database fetch operations have a very common (to my app) use case where the user wants to compare two fields, usually as "FIELD1 < FIELD2 OR FIELD1 > FIELD3"

I'd like to add a plugin adding additional 'field comparison' operators (one for each of the tradition operators, but specifying a field comparison rather that comparison to an explicit value) that, when one of these operators is selected, will trigger a rule's value to render an additional column/field selection, so that the two columns can be compared by the users selected operator.

I'd also like to integrate with the SQL parser so that queries containing column to column comparisons can be parsed by the SQL parser and rendered as rules in the SQL builder.

I know I need to perform some operations on the
afterUpdateRuleOperator.queryBuilder
event, but not sure where to go from there.

Start with the afterUpdateRuleOperator.queryBuilder event mentioned in the issue and trace how operators render their rule values and how the SQL parser produces rules. Define the column-comparison operators and their additional field selection, then integrate parsing and SQL-builder rendering. Done means column-to-column comparisons work through both the UI and SQL parser.