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1. 递归查询说明

Oracle

-- 使用递归查询获取员工的所有下属
WITH subordinates (employee_id, subordinate_id, level) AS (
  SELECT employee_id, subordinate_id, 1
  FROM employee
  WHERE employee_id = 1 -- 以员工ID为1为例
  UNION ALL
  SELECT e.employee_id, e.subordinate_id, s.level + 1
  FROM employee e
  JOIN subordinates s ON e.employee_id = s.subordinate_id
)
SELECT employee_id, subordinate_id, level
FROM subordinates;

Oracle使用WITH关键字来创建递归查询，首先查询出初始条件（即以某个员工ID为起点），然后通过UNION ALL将其和子查询（即下属）拼接起来，直到查询出所有下属。

MySQL

-- 使用递归查询获取员工的所有下属
WITH RECURSIVE subordinates (employee_id, subordinate_id, level) AS (
  SELECT employee_id, subordinate_id, 1
  FROM employee
  WHERE employee_id = 1 -- 以员工ID为1为例
  UNION ALL
  SELECT e.employee_id, e.subordinate_id, s.level + 1
  FROM employee e
  JOIN subordinates s ON e.employee_id = s.subordinate_id
)
SELECT employee_id, subordinate_id, level
FROM subordinates;

MySQL使用WITH RECURSIVE关键字来创建递归查询，其语法与Oracle类似。

SQL Server

-- 使用递归查询获取员工的所有下属
WITH subordinates (employee_id, subordinate_id, level) AS (
  SELECT employee_id, subordinate_id, 1
  FROM employee
  WHERE employee_id = 1 -- 以员工ID为1为例
  UNION ALL
  SELECT e.employee_id, e.subordinate_id, s.level + 1
  FROM employee e
  JOIN subordinates s ON e.employee_id = s.subordinate_id
)
SELECT employee_id, subordinate_id, level
FROM subordinates;

SQL Server也使用WITH关键字来创建递归查询，其语法与Oracle类似。

PostGreSQL

-- 使用递归查询获取员工的所有下属
WITH RECURSIVE subordinates (employee_id, subordinate_id, level) AS (
  SELECT employee_id, subordinate_id, 1
  FROM employee
  WHERE employee_id = 1 -- 以员工ID为1为例
  UNION ALL
  SELECT e.employee_id, e.subordinate_id, s.level + 1
  FROM employee e
  JOIN subordinates s ON e.employee_id = s.subordinate_id
)
SELECT employee_id, subordinate_id, level
FROM subordinates;

PostGreSQL也使用WITH RECURSIVE关键字来创建递归查询，其语法与MySQL类似。

2. 多表递归查询示例

建表语句和数据插入语句

-- 创建部门表
CREATE TABLE department (
  department_id INTEGER PRIMARY KEY,
  department_name VARCHAR(50),
  parent_department_id INTEGER
);

-- 插入部门数据
INSERT INTO department VALUES (1, '总公司', NULL);
INSERT INTO department VALUES (2, '财务部', 1);
INSERT INTO department VALUES (3, '人力资源部', 1);
INSERT INTO department VALUES (4, '财务部1', 2);
INSERT INTO department VALUES (5, '财务部2', 2);
INSERT INTO department VALUES (6, '人力资源部1', 3);
INSERT INTO department VALUES (7, '人力资源部2', 3);

-- 创建员工表
CREATE TABLE employee (
  employee_id INTEGER PRIMARY KEY,
  employee_name VARCHAR(50),
  department_id INTEGER REFERENCES department(department_id)
);

-- 插入员工数据
INSERT INTO employee VALUES (1, '张三', 2);
INSERT INTO employee VALUES (2, '李四', 2);
INSERT INTO employee VALUES (3, '王五', 4);
INSERT INTO employee VALUES (4, '赵六', 5);
INSERT INTO employee VALUES (5, '钱七', 6);
INSERT INTO employee VALUES (6, '孙八', 7);

Oracle多表递归查询

-- 使用递归查询获取部门的所有下级部门
WITH subdepartments (department_id, sub_department_id, level) AS (
  SELECT department_id, department_id, 1
  FROM department
  WHERE department_id = 1 -- 以总公司为例
  UNION ALL
  SELECT d.department_id, sd.sub_department_id, s.level + 1
  FROM department d
  JOIN subdepartments s ON d.parent_department_id = s.sub_department_id
  JOIN subdepartments sd ON d.department_id = sd.department_id
)
SELECT department_id, sub_department_id, level
FROM subdepartments;

MySQL多表递归查询

-- 使用递归查询获取部门的所有下级部门
WITH RECURSIVE subdepartments (department_id, sub_department_id, level) AS (
  SELECT department_id, department_id, 1
  FROM department
  WHERE department_id = 1 -- 以总公司为例
  UNION ALL
  SELECT d.department_id, sd.sub_department_id, s.level + 1
  FROM department d
  JOIN subdepartments s ON d.parent_department_id = s.sub_department_id
  JOIN subdepartments sd ON d.department_id = sd.department_id
)
SELECT department_id, sub_department_id, level
FROM subdepartments;

SQL Server多表递归查询

-- 使用递归查询获取部门的所有下级部门
WITH subdepartments (department_id, sub_department_id, level) AS (
  SELECT department_id, department_id, 1
  FROM department
  WHERE department_id = 1 -- 以总公司为例
  UNION ALL
  SELECT d.department_id, sd.sub_department_id, s.level + 1
  FROM department d
  JOIN subdepartments s ON d.parent_department_id = s.sub_department_id
  JOIN subdepartments sd ON d.department_id = sd.department_id
)
SELECT department_id, sub_department_id, level
FROM subdepartments;

PostGreSQL多表递归查询

-- 使用递归查询获取部门的所有下级部门
WITH RECURSIVE subdepartments (department_id, sub_department_id, level) AS (
  SELECT department_id, department_id, 1
  FROM department
  WHERE department_id = 1 -- 以总公司为例
  UNION ALL
  SELECT d.department_id, sd.sub_department_id, s.level + 1
  FROM department d
  JOIN subdepartments s ON d.parent_department_id = s.sub_department_id
  JOIN subdepartments sd ON d.department_id = sd.department_id
)
SELECT department_id, sub_department_id, level
FROM subdepartments;