1.查询与141号或174号员工的manager_id和department_id相同的其他员工的employee_id, manager_id, department_id (做对)
SELECT employee_id, manager_id, department_id
FROM employees
WHERE manager_id IN
(SELECT manager_id
FROM employees
WHERE employee_id IN (174,141))
AND department_id IN
(SELECT department_id
FROM employees
WHERE employee_id IN (174,141))
AND employee_id NOT IN(174,141);
2.返回比本部门平均工资高的员工的last_name, department_id, salary及平均工资
# 正确答案
SELECT a.t_name, a.salary,
a.department_id, b.salavg
FROM employees a, (SELECT department_id,
AVG(salary) salavg
FROM employees
GROUP BY department_id) b
WHERE a.department_id = b.department_id
AND a.salary > b.salavg;
# 自己思路优点bug
SELECT e1.last_name,e1.department_id,e1.salary,avg(e1.salary)
FROM employees e1,employees e2
WHERE e1.empoyee_id = e2.empoyee_id
AND e1.salary > (SELECT avg(salary) FROM employees e2
GROUP BY e2.department_id )
3. 显式员工的employee_id,last_name和location。其中,若员工department_id与location_id为1800的department_id相同,则location为’Canada’,其余则为’USA’
SELECT e.employee_id,e.last_name,
(CASE d.department_id WHEN (
SELECT department_id FROM departments
WHERE location_id = 1800) THEN 'Canada'
ELSE 'USA'
END) location
FROM empoyees e,department d
WHERE e.department_id = d.department_id;
# 自己写的
SELECT e.employee_id,e.last_name,
(CASE WHEN d.department_id =
(SELECT department_id FROM departments
WHERE location_id = 1800) THEN 'Canada'
ELSE 'USA'
END) location
FROM empoyees e,department d
WHERE e.department_id = d.department_id;
感觉也对吧。。。
4.查询员工的employee_id,t_name,要求按照员工的department_name排序
#答案
SELECT employee_id, t_name
FROM employees e
ORDER BY (SELECT department_name
FROM departments d
WHERE e.department_id = d.department_id);
CREATE TABLE em(
e_id INT NOT NULL,
name VARCHAR(15) NOT NULL,
d_id INT NOT NULL);
CREATE TABLE de(
d_id INT NOT NULL,
d_name VARCHAR(15) NOT NULL
);
INSERT INTO em VALUES (1,'BOb',1);
INSERT INTO em VALUES (2,'John',2);
INSERT INTO em VALUES (3,'mary',2);
INSERT INTO em VALUES (4,'kylin',2);
INSERT INTO em VALUES (5,'lych',1);
INSERT INTO em VALUES (6,'echo',3);
INSERT INTO em VALUES (7,'linda',3);
INSERT INTO de VALUES (1,'A');
INSERT INTO de VALUES (2,'B');
INSERT INTO de VALUES (3,'C');
# 答案做法
SELECT e_id, name
FROM em e
ORDER BY (SELECT d_name
FROM de d
WHERE e.d_id = d.d_id);
#我的做法
SELECT e.e_id, e.name
FROM em e,de d
WHERE e.d_id = d.d_id
ORDER BY d.d_name;
最后的返回结果都对
但是我需要好好理解一下答案的做法
执行顺序from-where-group by-having-select-distinct-union-order by