ORACLE SQL查询获取前3名薪水rownum大于

Question

I want to write a query to display employees getting top 3 salaries

  SELECT *
    FROM (SELECT salary, first_name
            FROM employees
        ORDER BY salary desc)
   WHERE rownum <= 3;

But I dont understand how this rownum is calculated for the nested query will this work or if it has problem ,request you to please make me understand:

SELECT *
  FROM (SELECT salary, first_name 
          FROM employees
      ORDER BY salary )
 WHERE rownum >= 3;

I went through this link Oracle/SQL: Why does query "SELECT * FROM records WHERE rownum >= 5 AND rownum <= 10" - return zero rows ,but it again points to a link, which does not gives the answer

Answer 1

a_horse_with_no_name's answer is a good one,
but just to make you understand why you're 1st query works and your 2nd doesn't:

When you use the subquery, Oracle doesn't magically use the rownum of the subquery , it just gets the data ordered so it gives the rownum accordingly, the first row that matches criteria still gets rownum 1 and so on. This is why your 2nd query still returns no rows.

If you want to limit the starting row, you need to keep the subquery's rownum, ie:

SELECT *
FROM (SELECT * , rownum rn
  FROM (SELECT salary, first_name
          FROM employees
      ORDER BY salary ) )sq
WHERE sq.rn >= 3;

But as a_horse_with_no_name said there are better options ...

EDIT: To make things clearer, look at this query:

with t as (
select 'a' aa, 4 sal from dual
union all
select 'b' aa, 1 sal from dual
union all
select 'c' aa, 5 sal from dual
union all
select 'd' aa, 3 sal from dual
union all
select 'e' aa, 2 sal from dual
order by aa
)
select sub.*, rownum main_rn 
  from (select t.*, rownum sub_rn from t order by sal) sub 
 where rownum < 4

note the difference between the sub rownum and the main rownum, see which one is used for criteria

Answer 2

The "rownum" of a query is assigned before an order by is applied to the result. So the rownumw 42 could wind up being the first row.

Generally speaking you need to use the rownum from the inner query to limit your overall output. This is very well explained in the manual:

http://docs.oracle.com/cd/E11882_01/server.112/e26088/pseudocolumns009.htm#i1006297

I prefer using row_number() instead, because you have much better control over the sorting and additionally it's a standard feature that works on most modern DBMS:

SELECT *
FROM (
  SELECT salary, 
         first_name, 
         row_number() over (order by salary) as rn
  FROM employees
)
WHERE rn <= 3
ORDER BY salary;

You should understand that the derived table in this case is only necessary to be able to apply a condition on the generated rn column. It's not there to avoid the "rownum problem" as the value of row_number() only depends on the order specifiy in the over(...) part (it is independent of any ordering applied to the query itself)

Note this would not return employees that have the same salary and would still fall under the top three. In that case using dense_rank() is probably more approriate.

Answer 3

if you want to select the people with the top 3 salaries.. perhaps you should consider using analytics.. something more like

SELECT *
FROM (
    SELECT salary, first_name, dense_rank() over(order by salary desc) sal_rank
    FROM employees 
)
WHERE  sal_rank <= 3

ie ALL people with the 3rd highest(ranked) salary amount(or more)

the advantage of this over using plain rownum is if you have multiple people with the same salary they will all be returned.

Answer 4

Easiest way to print 5th highest salary.

SELECT MIN(SALARY) FROM (SELECT SALARY FROM EMPLOYEES ORDER BY DESC) WHERE ROWNUM BETWEEN 1 AND 5 

according to same if u want to print 3rd or 4th highest salary then just chage last value.(means instead of 5 use 3 or 4 you will get 3rd or 4th highest salary).

SELECT MIN(SALARY) FROM (SELECT SALARY FROM EMPLOYEES ORDER BY DESC) WHERE ROWNUM BETWEEN 1 AND 4

SELECT MIN(SALARY) FROM (SELECT SALARY FROM EMPLOYEES ORDER BY DESC) WHERE ROWNUM BETWEEN 1 AND 3

Answer 5

SELECT EMPNO，SAL（从E.EMPNO <= T.EMPNO的测试中选择SUM（E.SAL），R_SAL FROM（SELECT EMPNO，EMPNO的测试订单中的SAL）T

Answer 6

Easiest way to find the top 3 employees in oracle returning all fields details:

SELECT *
FROM (
    SELECT * FROM emp  
      ORDER BY sal DESC)
WHERE rownum <= 3 ;

Answer 7

select * 
from (
    select emp.*, 
           row_number() over(order by sal desc)r 
    from emp
) 
where r <= 3;

Answer 8

SELECT Max(Salary)
FROM Employee
WHERE Salary < (SELECT Max(salary) FROM employee WHERE Salary NOT IN (SELECT max(salary) FROM employee))
ORDER BY salary DESC;