Exercise 2: No Workaround Needed in Raw SQL — Possible Solution
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THE ASTRO REBUILD'S OWN DRIZZLE WORKAROUND
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Per the Astro rebuild's Chapter 2, Drizzle's schema needed:

  parentId: int('parent_id').references(
    (): AnyMySqlColumn => pages.id,
    { onDelete: 'restrict' }
  )

- a function wrapper around the reference, specifically because pages
couldn't be referenced directly from inside its own definition while
TypeScript was still evaluating the pages constant itself.

THE RAW SQL EQUIVALENT, NO WORKAROUND NEEDED
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  FOREIGN KEY (parent_id) REFERENCES pages(id) ON DELETE RESTRICT

This line reads and applies with no special syntax, no function
wrapper, and no circular-reference concern at all - it's declared
directly inside the same CREATE TABLE pages statement.

WHY THE DIFFERENCE EXISTS
------------------------------
SQL DDL isn't evaluated as a sequence of interdependent expressions
the way a TypeScript object literal is - the CREATE TABLE statement
is parsed as a whole by the database engine, so a table referencing
its own not-yet-fully-defined self is simply the normal, expected
shape of a self-referencing table, not a special case at all.

WHY THIS WORKS AS AN ANSWER
------------------------------
It correctly restates Drizzle's own real workaround from the Astro
rebuild, correctly shows the equivalent raw SQL needing none, and
correctly explains why the underlying language/format difference (SQL
DDL vs. evaluated TypeScript) is what causes the difference.