why the below query take too much time.

Dear all ,

I design a query for Item Cost Aging Report in EBS R12 , but it take too much time , when i run this query for item it showing correct result and when i run this query for specific category the it take too much extra time . Anyone can help me what is missing join .

select category  , sum(CVal) total_cost ,

SUM(CASE WHEN days >=0  AND   days<=30 THEN CVal ELSE 0 END) DAYS_30,

SUM(CASE WHEN days >=31  AND   days<=90 THEN CVal ELSE 0 END) DAYS_90,

SUM(CASE WHEN days >=91  AND   days<=180 THEN CVal ELSE 0 END) DAYS_180,

SUM(CASE WHEN days >=181  AND   days<=360 THEN CVal ELSE 0 END) DAYS_360,