Implemented selecting and joining a subquery. Example usage:

const sq = db
  .select({
    categoryId: courseCategoriesTable.id,
    category: courseCategoriesTable.name,
    total: sql`count(${courseCategoriesTable.id})`.as<number>(),
  })
  .from(courseCategoriesTable)
  .groupBy(courseCategoriesTable.id, courseCategoriesTable.name)
  .subquery('sq');

After that, just use the subquery instead of a table as usual.

❗ Replaced db.select(table).fields({ ... }) syntax with db.select({ ... }).from(table) to look more like its SQL counterpart.