Lesson 20 · Parsing CREATE TABLE - Build a SQL Database

Parsing CREATE TABLE

The parser has read queries; now it reads schema. Today you parse a CREATE TABLE statement into a node listing each column's name and type.

The goal

Parse CREATE TABLE with a parenthesized list of typed columns into a create-table statement node.

Start here - the target

TO DO

Scenario: Parsing a CREATE TABLE statement

Giventhe statement "CREATE TABLE users (id INTEGER, name TEXT)"

Whenit is parsed

Thenthe result is a CreateTable for "users" with columns [(id, INTEGER), (name, TEXT)]

Andan unknown type keyword reports an error

Background

So far every statement has been a query; CREATE TABLE is the first that changes the database’s structure. This is exactly why Parse dispatched on the leading keyword back on lesson 15: today you add a second route. CREATE steers to a new parseCreate, and CreateStmt satisfies the same Stmt marker as SelectStmt, so nothing about Parse’s shape changes - you just slot in the case. Its grammar is a header - CREATE TABLE and a name - followed by a parenthesized, comma-separated list of column definitions, each a name and a type keyword. Parsing it reuses everything you have: expect for the fixed keywords and punctuation, an identifier for each name, and a small set of recognized type keywords (INTEGER, TEXT) mapping to the Kind values from lesson 1.

Rejecting an unknown type - id FLOATY - with a clear error is part of the job; the parser is the first place a nonsense schema should be caught. The Column type you built for the schema is exactly what these definitions produce, so the executor will be able to hand the list straight to CreateTable next chapter.

Make it work

type CreateStmt struct { Table string; Columns []Column } // also a Stmt
// add a CREATE case to Parse's keyword dispatch -> parseCreate
// parseCreate: expect(CREATE); expect(TABLE); table = expect(Identifier)
//   expect(LParen); loop: name=Identifier, type keyword (INTEGER|TEXT),
//   separated by commas; expect(RParen)

CheckpointDONE

The parser turns CREATE TABLE into a statement carrying its column definitions. Commit and stop here.