SQL

Parsing and Analysis

In the previous article, we explored how PostgreSQL establishes connections and communicates using its wire protocol. Once your connection is established and the backend process is ready, you can finally send queries. But when PostgreSQL receives your SQL, it’s just a string of text—the database can’t execute text directly.

Let me show you what happens when PostgreSQL receives this query:

SELECT name FROM users WHERE id = 42;

PostgreSQL doesn’t see this as a command yet. It sees characters: S, E, L, E, C, T, and so on. The journey from this raw text to something PostgreSQL can execute involves two major transformations: parsing (understanding structure) and semantic analysis (adding meaning).

Overview

Ever wonder what happens when you type SELECT * FROM users WHERE id = 42; and hit Enter? That simple query triggers a fascinating journey through PostgreSQL’s internals—a complex series of operations involving multiple processes, sophisticated memory management, and decades of optimization research.

This is the first article in a series where we’ll explore PostgreSQL’s query execution in depth. In this overview, I’ll walk you through the complete journey from SQL text to results, giving you the roadmap. Then, in subsequent articles, we’ll dive deep into each component—the parser, analyzer, rewriter, planner, and executor—exploring the details of how each one works.