查找當前薪水(to_date=‘9999-01-01’)排名第二多的員工編號emp_no、薪水salary、last_name以及first_name,不準使用order by
CREATE TABLE employees
(
emp_no
int(11) NOT NULL,
birth_date
date NOT NULL,
first_name
varchar(14) NOT NULL,
last_name
varchar(16) NOT NULL,
gender
char(1) NOT NULL,
hire_date
date NOT NULL,
PRIMARY KEY (emp_no
));
CREATE TABLE salaries
(
emp_no
int(11) NOT NULL,
salary
int(11) NOT NULL,
from_date
date NOT NULL,
to_date
date NOT NULL,
PRIMARY KEY (emp_no
,from_date
));
- 一個子查詢 + max()
select a.emp_no , max(b.salary) , a.last_name , a.first_name
from employees as a join salaries as b
on a.emp_no = b.emp_no
where b.to_date='9999-01-01'
and b.salary != (
select max(salary) from salaries where b.to_date='9999-01-01');
- 兩個子查詢max()
select a.emp_no , b.salary , a.last_name , a.first_name
from employees as a join salaries as b
on a.emp_no = b.emp_no
where b.to_date='9999-01-01' and b.salary = (
select max(salary) from salaries where salary != (
select max(salary) from salaries));
總結:
1.**查詢n條記錄中次高者,**不可以用order by時,可以選擇用子查詢的方式,先找到記錄中的最高者,然後父查詢中的where條件爲記錄中不爲子查詢結果的其他記錄的最高者max()。
2.當用order by時,可以用限定語句limit n-1,1找到次n高者;如果多條記錄中有重複值,可以考慮使用group by 或distinct(當查詢列爲多個時,採用子查詢distinct)的方式去重。