Gets the delete string for SQL deleting from the codomain of the pullback constraint, the element which is the codomain
of the element being deleted from the domain.
Gets the main path conditions to determine whether the pullback table contains elements along the path for
every element in the alternate table which leads to the same element as the main table.
Determines the last entity before the codomain of the path and sets the SELECT statement
to select the reference to the codomain of the path from this entity.