PostgreSQL Source Code interpretation (17)-query statement # 2 (query Optimization Foundation)
Projection push-down
Through the above conversion, the number of tuples before connection and the fields involved in the operation are reduced to achieve the purpose of optimization. IV. Summary
1. Equivalence rules: relational algebraic expressions can be transformed according to equivalence rules.
2. Optimization: the expression can be rewritten into a better equivalent expression through the equivalence rule.
V. reference
Wikipedia
Database system concept
