从路径组件创建路径字符串

Question

考虑下表包含有关目录结构的信息：

CREATE TABLE t (id INTEGER, name TEXT, parent INTEGER);
INSERT into t VALUES
(1, "", 1),
(2, "a", 1),
(3, "b", 2),
(4, "c", 3),
(5, "d", 1);

SELECT * FROM t;

从这个表中应该可以得到一个包含路径名的列

""
"a"
"a/b"
"a/b/c"
"d"

似乎某种递归是必要的。到目前为止，我只设法创建了父目录的文本列：

SELECT b.id, b.name name, b.parent parent, a.name as parent_name
FROM t a INNER JOIN t b ON a.id = b.parent;

如何从这里开始？

Answer 1

是的，您必须使用递归，这在 SQLite 中可以使用 WITH 来完成：

WITH RECURSIVE tf AS (
   SELECT id, name, parent, name AS full, parent AS p FROM t
UNION
    SELECT id, name, parent,
        (SELECT name FROM t WHERE id=tf.p) || "\" || full,
        (SELECT parent FROM t WHERE id=tf.p)
        FROM tf WHERE p IS NOT NULL
)
SELECT id, name, full FROM tf WHERE p IS NULL;