pgsql中层次查询方法

与Oracle中的start with ... connect by..非常相似的功能，查询后显示目录层次结构的方法：

当然在SQL Server 2005之后有with的功能。

测试代码：

DROP TABLE IF EXISTS t1;
CREATE TABLE t1(id integer primary key, 
                name varchar(32), 
                parent integer);

INSERT INTO t1 VALUES(1, '中国', 0);
INSERT INTO t1 VALUES(2, '江苏', 1);
INSERT INTO t1 VALUES(3, '浙江', 1);
INSERT INTO t1 VALUES(4, '上海', 1);
INSERT INTO t1 VALUES(5, '南京', 2);
INSERT INTO t1 VALUES(6, '苏州', 2);
INSERT INTO t1 VALUES(7, '杭州', 3);
INSERT INTO t1 VALUES(8, '宁波', 3);
INSERT INTO t1 VALUES(9, '昆山', 6);
INSERT INTO t1 VALUES(10,'常熟', 6);
INSERT INTO t1 VALUES(11,'吴江', 6);

实现代码：

WITH RECURSIVE X AS(SELECT t1.*, t1.id::text AS path 
                    FROM t1 
                    WHERE layer = 1
                    UNION ALL 
                    SELECT t1.*, path ||'|' ||  t1.id 
                    FROM t1 JOIN x 
                    ON t1.parent = x.id) 
SELECT * FROM x ORDER BY path; 

WITH RECURSIVE r AS ( 
       SELECT * FROM t1 WHERE id = 6
     UNION ALL 
       SELECT t1.* FROM t1, r WHERE t1.parent = r.id 
     ) 
SELECT * FROM r ORDER BY id;