When to use First instead of First_Value functions

Question

When would you use the First_Values function instead of First? What's the difference between the two?

Answer 1

Here are some examples of both in action. Use the analytic function FIRST_VALUE when you don't want to group your records. Use the aggregate function FIRST when you do.
select
  deptno ,
  hiredate ,
  ename ,
  first_value( ename ) over ( partition by deptno order by hiredate ) first_hired
from emp
order by deptno, hiredate ;
    DEPTNO HIREDATE   ENAME      FIRST_HIRE
        10 1981-06-09 CLARK      CLARK
        10 1981-11-17 KING       CLARK
        10 1982-01-23 MILLER     CLARK
        20 1980-12-17 SMITH      SMITH
        20 1981-04-02 JONES      SMITH
        20 1981-12-03 FORD       SMITH
        20 1987-04-19 SCOTT      SMITH
        20 1987-05-23 ADAMS      SMITH
        30 1981-02-20 ALLEN      ALLEN
        30 1981-02-22 WARD       ALLEN
        30 1981-05-01 BLAKE      ALLEN
        30 1981-09-08 TURNER     ALLEN
        30 1981-09-28 MARTIN     ALLEN
        30 1981-12-03 JAMES      ALLEN
14 rows selected.
select
  deptno,
  min(ename) keep ( dense_rank first order by hiredate ) as first_hired
from emp
group by deptno
order by deptno ;
    DEPTNO FIRST_HIRE
        10 CLARK
        20 SMITH
        30 ALLEN
3 rows selected.As far as analytic FIRST_VALUE versus the analytic version of FIRST, FIRST_VALUE has the option to IGNORE NULLS whereas FIRST doesn't.
select
  deptno ,
  hiredate ,
  comm ,
  first_value( comm IGNORE NULLS ) over ( partition by deptno order by hiredate desc )
    as first_value ,
  min(comm) keep ( dense_rank first order by hiredate desc )
    over ( partition by deptno )
    as first
from emp
order by deptno, hiredate ;
    DEPTNO HIREDATE         COMM FIRST_VALUE      FIRST
        10 1981-06-09
        10 1981-11-17
        10 1982-01-23
        20 1980-12-17
        20 1981-04-02
        20 1981-12-03
        20 1987-04-19
        20 1987-05-23
        30 1981-02-20        300        1400
        30 1981-02-22        500        1400
        30 1981-05-01                   1400
        30 1981-09-08          0        1400
        30 1981-09-28       1400        1400
        30 1981-12-03
14 rows selected.Other than that the two seem functionally equivalent. I prefer FIRST_VALUE over FIRST though because its syntax is more familiar.
Joe Fuda
SQL Snippets
Message was edited by: SnippetyJoe - added third example