Faire des intervalles de temps, et en particulier faire des agrégations (sommes, moyennes) sur de nombreux intervalles ou groupes d'intervalles n'est pas simple dans Oracle. La fonction AVG ne fonctionne pas sur les intervalles d'horodatage, elle attend des nombres. Nous devrons donc créer notre propre objet et fonction d'agrégation qui fera cela.
Tout d'abord, la spécification de l'objet :
CREATE OR REPLACE TYPE AvgInterval
AS OBJECT (
runningSum INTERVAL DAY(9) TO SECOND(9),
runningCnt number,
STATIC FUNCTION ODCIAggregateInitialize
( actx IN OUT AvgInterval
) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateIterate
( self IN OUT AvgInterval,
val IN DSINTERVAL_UNCONSTRAINED
) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateTerminate
( self IN AvgInterval,
returnValue OUT DSINTERVAL_UNCONSTRAINED,
flags IN NUMBER
) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateMerge
(self IN OUT AvgInterval,
ctx2 IN AvgInterval
) RETURN NUMBER
);
Et le corps de l'objet :
CREATE OR REPLACE TYPE BODY AvgInterval AS
STATIC FUNCTION ODCIAggregateInitialize
( actx IN OUT AvgInterval
) RETURN NUMBER IS
BEGIN
IF actx IS NULL THEN
actx := AvgInterval (INTERVAL '0 0:0:0.0' DAY TO SECOND, 0);
ELSE
actx.runningSum := INTERVAL '0 0:0:0.0' DAY TO SECOND;
actx.runningCnt := 0;
END IF;
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateIterate
( self IN OUT AvgInterval,
val IN DSINTERVAL_UNCONSTRAINED
) RETURN NUMBER IS
BEGIN
self.runningSum := self.runningSum + val;
self.runningCnt := self.runningCnt + 1;
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateTerminate
( self IN AvgInterval,
ReturnValue OUT DSINTERVAL_UNCONSTRAINED,
flags IN NUMBER
) RETURN NUMBER IS
BEGIN
if (runningCnt <> 0) then
returnValue := (self.runningSum/runningCnt);
else
returnValue := self.runningSum;
end if;
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateMerge
(self IN OUT AvgInterval,
ctx2 IN AvgInterval
) RETURN NUMBER IS
BEGIN
self.runningSum := self.runningSum + ctx2.runningSum;
self.runningCnt := self.runningCnt + ctx2.runningCnt;
RETURN ODCIConst.Success;
END;
END;
Enfin, la fonction qui utilise l'objet ci-dessus :
CREATE OR REPLACE FUNCTION avg_interval( x DSINTERVAL_UNCONSTRAINED)
RETURN DSINTERVAL_UNCONSTRAINED PARALLEL_ENABLE
AGGREGATE USING AvgInterval;
Maintenant, nous pouvons l'utiliser comme ça :
with x as (
select systimestamp - 1/24 as created_date, systimestamp as modified_date from dual
union
select systimestamp - 2/24 as created_date, systimestamp as modified_date from dual
union
select systimestamp - 3/24 as created_date, systimestamp as modified_date from dual
)
select avg_interval(modified_date - created_date)
from x;
Sortie :
+00 02:00:00.562669
Nous pouvons également agréger plus de groupes avec ça :
with x as (
select 'FL' as state, to_dsinterval('0 00:56:30') as duration from dual
union
select 'FL' as state, to_dsinterval('0 02:08:40') as duration from dual
union
select 'GA' as state, to_dsinterval('0 01:01:00') as duration from dual
)
select state, avg_interval(duration)
from x
group by state;
Sortie :
FL +00 01:32:35.000000
GA +00 01:01:00.000000