FIRST_VALUE and LAST_VALUE Analytic Functions
This article gives an overview of the FIRST_VALUE and LAST_VALUE analytic functions.
Related articles.
- Analytic Functions
- RANK, DENSE_RANK, FIRST and LAST Analytic Functions
- LAG and LEAD Analytic Functions
- LISTAGG Analystic Function in 11g Release 2
- Top-N Queries
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.
For more information see:
- Analytic Functions
- RANK, DENSE_RANK, FIRST and LAST Analytic Functions
- LAG and LEAD Analytic Functions
- LISTAGG Analystic Function in 11g Release 2
- Top-N Queries
- Analytic Functions (Docs)
- FIRST_VALUE
- LAST_VALUE
Hope this helps. Regards Tim...
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