emp table in mysql 的递归结果

Question

我试图在 mysql 中获取递归结果，而不是在 mysql 5.X 中使用递归功能作为实例。

这是 emp table

的创建 table 和插入脚本

DROP TABLE IF EXISTS emp;

CREATE TABLE emp (
  empno decimal(4,0) NOT NULL,
  ename varchar(10) default NULL,
  job varchar(9) default NULL,
  mgr decimal(4,0) default NULL,
  hiredate date default NULL,
  sal decimal(7,2) default NULL,
  comm decimal(7,2) default NULL,
  deptno decimal(2,0) default NULL
);



INSERT INTO emp VALUES ('7369','SMITH','CLERK','7902','1980-12-17','800.00',NULL,'20');
INSERT INTO emp VALUES ('7499','ALLEN','SALESMAN','7698','1981-02-20','1600.00','300.00','30');
INSERT INTO emp VALUES ('7521','WARD','SALESMAN','7698','1981-02-22','1250.00','500.00','30');
INSERT INTO emp VALUES ('7566','JONES','MANAGER','7839','1981-04-02','2975.00',NULL,'20');
INSERT INTO emp VALUES ('7654','MARTIN','SALESMAN','7698','1981-09-28','1250.00','1400.00','30');
INSERT INTO emp VALUES ('7698','BLAKE','MANAGER','7839','1981-05-01','2850.00',NULL,'30');
INSERT INTO emp VALUES ('7782','CLARK','MANAGER','7839','1981-06-09','2450.00',NULL,'10');
INSERT INTO emp VALUES ('7788','SCOTT','ANALYST','7566','1982-12-09','3000.00',NULL,'20');
INSERT INTO emp VALUES ('7839','KING','PRESIDENT',NULL,'1981-11-17','5000.00',NULL,'10');
INSERT INTO emp VALUES ('7844','TURNER','SALESMAN','7698','1981-09-08','1500.00','0.00','30');
INSERT INTO emp VALUES ('7876','ADAMS','CLERK','7788','1983-01-12','1100.00',NULL,'20');
INSERT INTO emp VALUES ('7900','JAMES','CLERK','7698','1981-12-03','950.00',NULL,'30');
INSERT INTO emp VALUES ('7902','FORD','ANALYST','7566','1981-12-03','3000.00',NULL,'20');
INSERT INTO emp VALUES ('7934','MILLER','CLERK','7782','1982-01-23','1300.00',NULL,'10');

我想看到这样的结果

"ENAME" "BOSS"  "EMPNO" "PRIORENAME"    "LEVEL"
"king"  NULL    7839      ""              1
"jones" 7839    7566    "king"  2
"blake" 7839    7698    "king"  2
"clark" 7839    7782    "king"  2
"ford"  7566    7902    "jones" 3
"ward"  7698    7521    "blake" 3
"james" 7698    7900    "blake" 3
"miller"7782    7934    "clark" 3
"allen" 7698    7499    "blake" 3
"scott" 7566    7788    "jones" 3
"martin"7698    7654    "blake" 3
"turner"7698    7844    "blake" 3
"adams" 7788    7876    "scott" 4
"smith" 7902    7369    "ford"  4

我尝试了很多但不是很成功

Answer 1

MySQL 8.0 添加了对 CTE（常见 table 表达式）的支持，包括递归 CTE。在 8.0 之前的版本中（即 MySQL 5.x）没有对递归查询的原生支持。

使用 MySQL 5.x 有几种方法可以 returning 结果集（来自问题中提出的 table 的查询。）

一种方法是开发 MySQL 函数（存储程序），return “priorname” 和 “level” 值。

 SELECT t.ENAME
      , t.mgr                       AS `BOSS`
      , t.EMPNO
      , udf_emp_priorname(t.empno)  AS `PRIORNAME`
      , udf_emp_level(t.empno)      AS `LEVEL`
   FROM emp t
  ORDER BY ...

另一种方法是连接 return 级别 1、return 级别 2、return 级别 3 的单独查询的结果，向下有限数量的级别。

(
 SELECT t1.ENAME
      , t1.mgr     AS `BOSS`
      , t1.EMPNO
      , ''         AS `PRIORNAME`  
      , 1          AS `LEVEL`
   FROM emp t1
  WHERE t1.mgr IS NULL
)
UNION ALL
(
 SELECT t2.ENAME
      , t2.mgr     AS `BOSS`
      , t2.EMPNO
      , t1.ENAME   AS `PRIORNAME`  
      , 2          AS `LEVEL`
   FROM emp t1
   JOIN emp t2 ON t2.mgr = t1.EMPNO
  WHERE t1.mgr IS NULL
)
UNION ALL
(
 SELECT t3.ENAME
      , t3.mgr     AS `BOSS`
      , t3.EMPNO
      , t2.ENAME   AS `PRIORNAME`  
      , 3          AS `LEVEL`
   FROM emp t1
   JOIN emp t2 ON t2.mgr = t1.EMPNO
   JOIN emp t3 ON t3.mgr = t2.EMPNO
  WHERE t1.mgr IS NULL
)

emp table in mysql 的递归结果

The recursive result of emp table in mysql

mysql

hierarchical-data

recursive-query