New column type: SQLExpression
Currently some expressions that could be easily written in SQL are done using a Function field with a getter and quite often a searcher.
One drawback of this method is that if the field is search mulitple times then it results in numerous subqueries which performance-wise a bad idea.
So for simple expressions we could use a new column type that would return the SQL expression to use.
This is the goal of of the related review.