如何翻譯嵌套的CASE表達式以理解邏輯？

Question

我有一個由其他人創建的存儲過程。在WHERE條款，還有的是，我有一個很難理解一個CASE表達式：

DECLARE 
     @DateFrom datetime = '01-01-2016', 
     @DateTo datetime = '12-31-2016' 
     @EffDateFrom datetime = NULL, 
     @EffDateTo datetime = NULL, 
    /* SOME SELECT statement here */ 
WHERE  
      CASE WHEN @EffDateFrom IS NULL THEN 1 
          ELSE CASE WHEN dateDiff(d, '01-01-2016', dbo.tblQuotes.EffectiveDate) >= 0 
            AND dateDiff(d, EOMONTH (GETDATE()), dbo.tblQuotes.EffectiveDate) <= 0 Then 1 
            else 0 
            end 
          END = 1 

--------------/* This is where I am confused */-------------------------------- 

         AND CASE WHEN @DateFrom IS NULL THEN 1 ELSE 
          CASE WHEN INV.InvoiceDate > INV.EffectiveDate THEN 
           CASE WHEN dateDiff(d, '01-01-2016', INV.InvoiceDate) >= 0 
            AND dateDiff(d, '12-31-2016', INV.InvoiceDate) <= 0 Then 1 else 0 end 
          ELSE 
           CASE WHEN dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0 
            AND dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0 Then 1 else 0 end 
          END 
          END = 1 

所以我們在這裏說的是：

當參數@DateFrom爲null，則使用參數@EffDateFrom ， 是對的嗎？

但是，如果其不爲空，然後 1，檢查InvoiceDate大於EFFECTIVEDATE，如果它是 - 然後 2.檢查是否01-01-2016和InvoiceDate之間的天數大於或等於0 AND如果該號碼12-31-2016與InvoiceDate之間的天數小於或等於0，則爲1！什麼是1？這意味着記錄是有效的？記錄將在一張桌子上？正確？

而且ELSE 0這意味着它不會接的記錄，是否正確？

之後，我很困惑。 更新的理解（如果正確）：

CASE WHEN @DateFrom IS NULL THEN 1 ELSE 

          CASE WHEN INV.InvoiceDate > INV.EffectiveDate THEN 
-----------------------------/*then check the below conditions and if its 1 then display the record if its 0 then do NOT */ 
             CASE WHEN dateDiff(d, '01-01-2016', INV.InvoiceDate) >= 0 
                AND dateDiff(d, '12-31-2016', INV.InvoiceDate) <= 0 THEN 1 ELSE 0 
             END 
----------------------------/* and this statement will only be working if parameter @EffDateFrom is not null. Correct? */ 
          ELSE 
           CASE WHEN dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0 
            AND dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0 Then 1 else 0 end 
          END 
          END = 1 

Answer 1

這是（部分的你問）的邏輯：

IF (@DateFrom IS NULL) 
    OR ((INV.InvoiceDate > INV.EffectiveDate) AND (dateDiff(d, '01-01-2016', INV.InvoiceDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.InvoiceDate) <= 0)) 
    OR ((INV.InvoiceDate <= INV.EffectiveDate) AND (dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0)) 
    OR ((INV.InvoiceDate IS NULL) AND (dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0)) 
    OR ((INV.EffectiveDate IS NULL) AND (dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0)) 
THEN TRUE 
ELSE FALSE 

整個聲明：

IF (@EffDateFrom IS NULL) 
    OR ((dateDiff(d, '01-01-2016', dbo.tblQuotes.EffectiveDate) >= 0) AND (dateDiff(d, EOMONTH (GETDATE()), dbo.tblQuotes.EffectiveDate) <= 0)) 
THEN TRUE 
ELSE FALSE 

AND 

IF (@DateFrom IS NULL) 
    OR ((INV.InvoiceDate > INV.EffectiveDate) AND (dateDiff(d, '01-01-2016', INV.InvoiceDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.InvoiceDate) <= 0)) 
    OR ((INV.InvoiceDate <= INV.EffectiveDate) AND (dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0)) 
    OR ((INV.InvoiceDate IS NULL) AND (dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0)) 
    OR ((INV.EffectiveDate IS NULL) AND (dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0) AND (dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0)) 
THEN TRUE 
ELSE FALSE 

Answer 2

零件時，感到困惑可以被解釋爲以下無需使用case語句：

WHERE 
      @DateFrom IS NULL 

OR ( @DateFrom IS NOT NULL 
     AND INV.InvoiceDate > INV.EffectiveDate 
     AND dateDiff(d, '01-01-2016', INV.InvoiceDate) >= 0 
     AND dateDiff(d, '12-31-2016', INV.InvoiceDate) <= 0 
    ) 

OR ( @DateFrom IS NOT NULL 
     AND dateDiff(d, '01-01-2016', INV.EffectiveDate) >= 0 
     AND dateDiff(d, '12-31-2016', INV.EffectiveDate) <= 0 
    )