Analytic Function RANK, DENSE_RANK, FIRST and LAST

This article gives and overview of the RANK, DENSE_RANK, FIRST and LAST analytic functions:-
• RANK
• DENSE_RANK
• FIRST and LAST

RANK:
Let's assume we want to assign a sequential order, or rank, to people within a department based on salary, we might use the RANK function like.

SELECT empno, deptno, sal, 
RANK() OVER (PARTITION BY deptno ORDER BY sal) "rank"
FROM emp;

EMPNO DEPTNO SAL rank
---------- ---------- ---------- ----------
7934 10 1300 1
7782 10 2450 2
7839 10 5000 3
7369 20 800 1
7876 20 1100 2
7566 20 2975 3
7788 20 3000 4
7902 20 3000 4
7900 30 950 1
7654 30 1250 2
7521 30 1250 2
7844 30 1500 4
7499 30 1600 5
7698 30 2850 6

SQL>

What we see here is where two people have the same salary they are assigned the same rank. When multiple rows share the same rank the next rank in the sequence is not consecutive.

DENSE_RANK:
The DENSE_RANK function acts like the RANK function except that it assigns consecutive ranks.

SELECT empno, deptno, sal,
DENSE_RANK() OVER (PARTITION BY deptno ORDER BY sal) "rank"
FROM emp;

EMPNO DEPTNO SAL rank
---------- ---------- ---------- ----------
7934 10 1300 1
7782 10 2450 2
7839 10 5000 3
7369 20  800 1
7876 20 1100 2
7566 20 2975 3
7788 20 3000 4
7902 20 3000 4
7900 30  950 1
7654 30 1250 2
7521 30 1250 2
7844 30 1500 3
7499 30 1600 4
7698 30 2850 5

SQL>

FIRST and LAST:
The FIRST and LAST functions can be used to return the first or last value from an ordered sequence. Say we want to display the salary of each employee, along with the lowest and highest within their department we may use something like.

SELECT empno, deptno, sal,
MIN(sal) KEEP (DENSE_RANK FIRST ORDER BY sal) OVER (PARTITION BY deptno) "Lowest",
MAX(sal) KEEP (DENSE_RANK LAST ORDER BY sal) OVER (PARTITION BY deptno) "Highest"
FROM emp
ORDER BY deptno, sal;

EMPNO DEPTNO SAL Lowest Highest
---------- ---------- ---------- ---------- ----------
7934 10 1300 1300 5000
7782 10 2450 1300 5000
7839 10 5000 1300 5000
7369 20 800 800 3000
7876 20 1100 800 3000
7566 20 2975 800 3000
7788 20 3000 800 3000
7902 20 3000 800 3000
7900 30 950 950 2850
7654 30 1250 950 2850
7521 30 1250 950 2850
7844 30 1500 950 2850
7499 30 1600 950 2850
7698 30 2850 950 2850

FIRST_VALUE and LAST_VALUE Analytic Functions:

This article gives an overview of the FIRST_VALUE and LAST_VALUE analytic functions.
• FIRST_VALUE
• LAST_VALUE

FIRST_VALUE:

The FIRST_VALUE analytic function is similar to the FIRST analytic function, allowing you to return the first result from an ordered set.

SELECT empno, deptno, sal,
FIRST_VALUE(sal) IGNORE NULLS 
OVER (PARTITION BY deptno ORDER BY sal) AS lowest_in_dept
FROM emp;

EMPNO DEPTNO SAL LOWEST_IN_DEPT
---------- ---------- ---------- --------------
7934 10 1300 1300
7782 10 2450 1300
7839 10 5000 1300
7369 20 800 800
7876 20 1100 800
7566 20 2975 800
7788 20 3000 800
7902 20 3000 800
7900 30 950 950
7654 30 1250 950
7521 30 1250 950
7844 30 1500 950
7499 30 1600 950
7698 30 2850 950

SQL>

The "{RESPECT | IGNORE} NULLS" clause indicates if NULLs are considered when determining results.

The windowing clause can be used to alter the window of operation. The following example uses "ROWS 1 PRECEDING" to give a result similar, but not quite the same, to a LAG of 1 row.

SELECT empno, deptno, sal,
FIRST_VALUE(sal) IGNORE NULLS
OVER (PARTITION BY deptno ORDER BY sal ROWS 1 PRECEDING) AS preceding_in_dept
FROM emp;

EMPNO DEPTNO SAL PRECEDING_IN_DEPT
---------- ---------- ---------- -----------------
7934 10 1300 1300
7782 10 2450 1300
7839 10 5000 2450
7369 20 800 800
7876 20 1100 800
7566 20 2975 1100
7788 20 3000 2975
7902 20 3000 3000
7900 30 950 950
7654 30 1250 950
7521 30 1250 1250
7844 30 1500 1250
7499 30 1600 1500
7698 30 2850 1600

SQL>

LAST_VALUE:

The LAST_VALUE analytic function is similar to the LAST analytic function, allowing you to return the last result from an ordered set. Using the default windowing clause the result can be a little unexpected.

SELECT empno, deptno, sal,
LAST_VALUE(sal) IGNORE NULLS
OVER (PARTITION BY deptno ORDER BY sal) AS highest_in_dept
FROM emp;

EMPNO DEPTNO SAL HIGHEST_IN_DEPT
---------- ---------- ---------- ---------------
7934 10 1300 1300
7782 10 2450 2450
7839 10 5000 5000
7369 20 800 800
7876 20 1100 1100
7566 20 2975 2975
7788 20 3000 3000
7902 20 3000 3000
7900 30 950 950
7654 30 1250 1250
7521 30 1250 1250
7844 30 1500 1500
7499 30 1600 1600
7698 30 2850 2850

SQL>

This is because the default windowing clause is "RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW", which in this example means the current row will always be the last value. Altering the windowing clause to "RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING" gives us the result we probably expected.

SELECT empno, deptno, sal,
LAST_VALUE(sal) IGNORE NULLS
OVER (PARTITION BY deptno ORDER BY sal RANGE BETWEEN
UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS highest_in_dept
FROM emp;

EMPNO DEPTNO SAL HIGHEST_IN_DEPT
---------- ---------- ---------- ---------------
7934 10 1300 5000
7782 10 2450 5000
7839 10 5000 5000
7369 20 800 3000
7876 20 1100 3000
7566 20 2975 3000
7788 20 3000 3000
7902 20 3000 3000
7900 30 950 2850
7654 30 1250 2850
7521 30 1250 2850
7844 30 1500 2850
7499 30 1600 2850
7698 30 2850 2850

SQL>

As with the previous function, the "{RESPECT | IGNORE} NULLS" clause indicates if NULLs are considered when determining results. The default action is RESPECT NULLS.