递归 CTE 树形查询

WITH RECURSIVE cat_tree AS (
  SELECT id, name, parent_id, 1 AS lvl
  FROM categories WHERE parent_id IS NULL
  UNION ALL
  SELECT c.id, c.name, c.parent_id, t.lvl + 1
  FROM categories c
  INNER JOIN cat_tree t ON c.parent_id = t.id
)
SELECT * FROM cat_tree ORDER BY lvl, id;