LAST_VALUE [analytic]
Lets you select the last value of a table or partition (determined by the window-order-clause) without having to use a self join. LAST_VALUE takes the last record from the partition after the window order clause. The function then computes the expression against the last record, and returns the results. This function is useful when you want to use the last value as a baseline in calculations.
Use LAST_VALUE() with the window-order-clause to produce deterministic results. If no window is specified for the current row, the default window is UNBOUNDED PRECEDING AND CURRENT ROW.
Tip
Due to default window semantics,LAST_VALUE does not always return the last value of a partition. If you omit Window frame clause from the analytic clause, LAST_VALUE operates on this default window. Although results can seem non-intuitive by not returning the bottom of the current partition, it returns the bottom of the window, which continues to change along with the current input row being processed. If you want to return the last value of a partition, use UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING. See examples below.
Behavior type
ImmutableSyntax
LAST_VALUE ( expression [ IGNORE NULLS ] ) OVER (
[ window-partition-clause ]
[ window-order-clause ]
[ window-frame-clause ] )
Parameters
expression- Expression to evaluate—for example, a constant, column, nonanalytic function, function expression, or expressions involving any of these.
IGNORE NULLS- Specifies to return the last non-null value in the set, or
NULLif all values areNULL. If you omit this option and the last value in the set is null, the function returnsNULL. OVER()- See Analytic Functions.
Examples
Using the schema defined in Window framing in Analyzing Data, the following query does not show the highest salary value by department; instead it shows the highest salary value by department by salary.
=> SELECT deptno, sal, empno, LAST_VALUE(sal)
OVER (PARTITION BY deptno ORDER BY sal) AS lv
FROM emp;
deptno | sal | empno | lv
--------+-----+-------+--------
10 | 101 | 1 | 101
10 | 104 | 4 | 104
20 | 100 | 11 | 100
20 | 109 | 7 | 109
20 | 109 | 6 | 109
20 | 109 | 8 | 109
20 | 110 | 10 | 110
20 | 110 | 9 | 110
30 | 102 | 2 | 102
30 | 103 | 3 | 103
30 | 105 | 5 | 105
If you include the window frame clause ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING, LAST_VALUE() returns the highest salary by department, an accurate representation of the information:
=> SELECT deptno, sal, empno, LAST_VALUE(sal)
OVER (PARTITION BY deptno ORDER BY sal
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS lv
FROM emp;
deptno | sal | empno | lv
--------+-----+-------+--------
10 | 101 | 1 | 104
10 | 104 | 4 | 104
20 | 100 | 11 | 110
20 | 109 | 7 | 110
20 | 109 | 6 | 110
20 | 109 | 8 | 110
20 | 110 | 10 | 110
20 | 110 | 9 | 110
30 | 102 | 2 | 105
30 | 103 | 3 | 105
30 | 105 | 5 | 105
For more examples, see FIRST_VALUE().