遞歸Oracle查詢

Question

我有三個表：

• 訂閱
  SubscriptionID
  SubscriptionName
  繼承（可以是NULL）

• SubscriptionOptions
  SubscriptionOptionID
  SubscriptionID
  OptionID
  OptionValue

• 選項
  OptionID
  OptionDefaultValue
  說明

我需要在多個選項的查詢和訂閱ID來傳遞，沿着這些東西行：

SELECT optionid, optionvalue WHERE subscriptionid = x AND options IN (a, b, c, d, e, f) 

只有我需要通過這樣的遞歸調用來實現通過邏輯的繼承：

if subscriptionoption exists for subscription id & optionid 
    use subscriptionoption.optionvalue in the row 
else 
    if inherits is not NULL 
     call this function using inherited subscription id 
    else 
     use options.optiondefaultvalue for that optionid 

Answer 1

要做到這一點的SQL，我想你需要把一個分層查詢。這是一個擺動，但我沒有能夠測試它。

SELECT optionID, NVL(MAX(optionValue), MAX(optionDefaultValue)) optionValue 
FROM (SELECT optionID, optionDefaultValue, subscriptionID, inherits 
     FROM options CROSS JOIN subscriptions 
     WHERE optionID IN (a,b,c,d,e,f) 
    ) 
    LEFT JOIN subscriptionOptions USING (optionId, subscriptionID) 
START WITH subscriptionID = x 
CONNECT BY PRIOR optionValue IS NULL 
     AND subscriptionID = PRIOR inherits 
     AND optionID = PRIOR optionID 
GROUP BY optionID 

另一種方法是編寫實現單個subscriptionID和optionID遞歸的邏輯函數，然後調用它像這樣：

SELECT optionID, NVL(getSubscriptionOption(x, optionID), optionDefaultValue) 
    FROM options 
    WHERE optionID IN (a,b,c,d,e,f) 

功能可能是這樣的：

FUNCTION getSubscriptionOption(pSubID NUMBER, pOptID NUMBER) 
    RETURN subscriptionOptions.optionValue%TYPE 
    IS 
    l_optionValue subscriptionOptions.optionValue%TYPE; 
    l_inherits subscriptionOptions.inherits%TYPE; 
    BEGIN 
    SELECT optionValue 
     INTO l_optionValue 
     FROM subscriptionOptions 
     WHERE subscriptionID = pSubID 
     AND optionID = pOptID; 
    RETURN l_optionValue; 
    EXCEPTION 
    WHEN no_data_found THEN 
     SELECT inherits 
     INTO l_inherits 
     FROM subscriptions 
     WHERE subscriptionID = pSubID; 
     IF inherits IS NULL THEN 
     RETURN NULL; 
     ELSE 
     RETURN getSubscriptionOption(l_inherits, pOptID); 
     END IF; 
    END; 

或者可以寫成使用循環而不是遞歸。