Strip the expression required to compute a single column out of the provided operator tree.
Alpha-rename the specified column in the specified tree.
The name of the column to rewrite.
Names to avoid renaming
The operator tree to rewrite
A 2-tuple: The new name of the renamed column, and the new operator tree
Safely join two columns together, even if there's some possibility that the two joins have non-overlapping columns.
The left hand side of the join to create
The right hand side of the join to create
A conflict-free join, and a list of renamings for the right-hand-side columns.