如何重寫此查詢而不重複SELECT子查詢

Question

我寫過這樣的查詢。它正在工作，並給我我想要的結果。
我有一個SELECT查詢來獲取CAR_AMOUNT和HOTEL_AMOUNT。
但是，我不得不重複同樣的SELECT查詢來獲取兩者的SUM。我無法使用別名。我怎樣才能避免這種情況？

SELECT B.EMPLOYEE_ID, 
     (select SUM(AMOUNT) 
     FROM travel_reimbursements_items 
     WHERE type = 'CAR' 
     AND travel_request_no = B.travel_request_no 
     AND STATUS='APPROVED') as CAR_AMOUNT, 
     (select SUM(AMOUNT) 
     FROM travel_reimbursements_items 
     WHERE type = 'HOTEL' 
     AND travel_request_no = B.travel_request_no 
     AND STATUS='APPROVED') as HOTEL_AMOUNT, 
     NVL((select SUM(AMOUNT) 
      FROM travel_reimbursements_items 
      WHERE type = 'CAR' 
      AND travel_request_no = B.travel_request_no 
      AND STATUS='APPROVED'),0) 
     +NVL((select SUM(AMOUNT) 
      FROM travel_reimbursements_items 
      WHERE type = 'HOTEL' 
      AND travel_request_no = B.travel_request_no 
      AND STATUS='APPROVED'),0) as TOTAL 
FROM TRAVEL_REQUEST_ITEM A 
    LEFT OUTER JOIN TRAVEL_REQUEST B 
     ON (B.TRAVEL_REQUEST_NO= A.TRAVEL_REQUEST_SR_NO) 

Answer 1

這應該在oracle中工作。

SELECT B.EMPLOYEE_ID, 
      SUM(CASE WHEN C.type = 'CAR' and C.STATUS='APPROVED' THEN C.AMOUNT ELSE 0 END) as CAR_AMOUNT, 
      SUM(CASE WHEN C.type = 'HOTEL' and C.STATUS='APPROVED' THEN C.AMOUNT ELSE 0 END) as HOTEL_AMOUNT, 
      SUM(CASE WHEN C.type IN ('CAR', 'HOTEL') and C.STATUS='APPROVED' THEN C.AMOUNT ELSE 0 END) as TOTAL 
FROM TRAVEL_REQUEST_ITEM A 
    LEFT OUTER JOIN TRAVEL_REQUEST B ON (B.TRAVEL_REQUEST_NO= A.TRAVEL_REQUEST_SR_NO) 
    LEFT OUTER JOIN TRAVEL_REIMBURSEMENTS_ITEMS C ON (C.TRAVEL_REQUEST_NO = A.TRAVEL_REQUEST_SR_NO) 
GROUP BY B.EMPLOYEE_ID 

只要做一個基於項目類型的條件金額。

Answer 2

select b.employee_id 
    , sum(case when c.type = 'CAR' then c.amount end) car_amount 
    , sum(case when c.type = 'HOTEL' then c.amount end) hotel_amount 
    , sum(c.amount) total 
    from travel_request_item a 
     left outer join travel_request b 
     on (b.travel_request_no= a.travel_request_sr_no) 
     left outer join travel_reimbursements_items c 
     on ( c.travel_request_no = b.travel_request_no 
      and c.type in ('CAR','HOTEL') 
      and c.status = 'APPROVED' 
      ) 
group by b.employee_id 

問候，
羅布。