Understanding SQL Parsing: Lexical Analysis, Syntax Analysis, and Practical Example
This article explains the fundamentals of SQL parsing, describing the roles of lexical analysis, syntax analysis, and visitors, and demonstrates the process with a concrete SELECT statement example, while also mentioning popular parsing libraries such as Druid and ANTLR.
SQL (Structured Query Language) is a language like any other, so parsing it follows the same principles as parsing programming languages, involving compiler‑theory concepts.
To parse a language you typically need three tools:
Lexer (lexical analyzer) : converts a character stream into a sequence of tokens.
Parser (syntax analyzer) : builds a structured, often tree‑based, representation such as an abstract syntax tree (AST) from the token sequence.
Visitor : traverses the AST to extract the information you need.
Below is a concrete example that walks through the parsing of a simple SQL statement.
Original SQL: SELECT id, name FROM test WHERE ID > 2 LIMIT 2; 1. Lexical Analysis
The lexer splits the statement into tokens, producing a token stream like:
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