The stack is the structure used in calcite to store a relational expression.
- build() - Pops the most recently created relational expression off the stack. See relational expression creation
- push(rel) -Pushes a relational expression onto the stack. Relational methods such as scan, above, call this method, but user code generally does not
- pushAll(collection) - Pushes a collection of relational expressions onto the stack
- peek() - Returns the relational expression most recently put onto the stack, but does not remove it