This page outlines the relationship between:
- SQL syntax clauses, from the PostgreSQL dialect
- Algebraic-relational operators, provided by theory
- Nodes in the data structure (memo) used to represent logical plans during optimizations, that we call "relational operators" or "nodes"Â
They are more diverse than what provided by relational algebra, because they aim to represent everything that's possible in PostgreSQL's dialect.
This can be inspected with EXPLAIN (OPT).
- Nodes in the tree used as data interface during optimizations and physical planning.
We aim to remote this data structure entirely at some point. It's not fundamentally needed.
These correspond semantically to abstract, relational "operators" and specifications of operational semantics which we call "processors" below. They are a historical artifact.
This can be currently inspected with EXPLAIN (PLAN), but we aim to remote this data structure entirely at some point.
We also colloquially call this "the logical plan" although be mindful that the other data structure used for optimizations above is also a logical plan. Say "planNode tree" in technical discussions to disambiguate.
- Nodes that represent data processing logic in the physical plan graph, also called "processors"
This can be inspected with EXPLAIN (DISTSQL).