Lesson 23 · Executing INSERT - Build a SQL Database

Executing INSERT

With tables you can create, the next step is putting data in them. Today you execute an INSERT node, turning its value expressions into a row and appending it.

The goal

Execute a parsed INSERT so its literal values become a validated row in the target table.

Start here - the target

TO DO

Scenario: Executing an INSERT statement

Givena database with table users(id INTEGER, name TEXT) and a parsed Insert of (1, 'alice')

Whenthe statement is executed

Thenthe users table has one row [1, "alice"]

Andinserting into a missing table "ghosts" reports a table-not-found error

Background

INSERT is the executor’s first data-writing case. The Insert node carries a list of literal expressions; convert each to a Value - an IntLit becomes an integer value, a StrLit a text value - collect them into a Row, and hand it to the table’s Insert, which reuses the schema validation from lesson 5. A row of the wrong shape is rejected here without any new code.

Two failures are worth handling explicitly: inserting into a table that does not exist (the Table lookup fails) and inserting a row that violates the schema (validation fails). Both return a clear error rather than corrupting the database. With CREATE and INSERT running, you can build up state; next you teach the executor to read it back with expressions.

Make it work

case InsertStmt:
  t, ok := db.Table(s.Table)          // not found -> error
  // convert each literal expr to a Value, build a Row
  // t.Insert(row) reuses lesson-5 validation

CheckpointDONE

The executor runs INSERT, adding validated rows through the parser. Commit and stop here.