與CASE和NULL檢查的地方

Question

我在WHERE子句中有CASE語句的問題。在我的查詢中，我想獲取日期前的行。日期檢查3列。 date1是不是NULL，所以我不需要有空檢查，但日期date2和date3可以是NULL，所以我想檢查空值，並相應地檢查日期條件。我嘗試了兩種方法，但無法弄清楚如何正確執行。你能幫我嗎？

查詢1：

SELECT * 
FROM 
    docs 
WHERE 
    date1 < '20120601' 
    AND CASE 
     WHEN date2 IS NOT NULL AND date3 IS NOT NULL THEN date2 < '20120601' 
     WHEN date2 IS NOT NULL AND date3 IS NULL THEN date2 < '20120601' 
     WHEN date2 IS NULL AND date3 IS NOT NULL THEN date3 < '20120601' 
    END 

這給錯誤時，第一個：Incorrect syntax near '<'.

我修改我的查詢到這一點：

SELECT * 
FROM 
    docs 
WHERE 
    date1 < '20120601' 
    AND CASE 
     WHEN date2 IS NOT NULL AND date3 IS NOT NULL AND date2 < '20120601' THEN TRUE 
     WHEN date2 IS NOT NULL AND date3 IS NULL AND date2 < '20120601' THEN TRUE 
     WHEN date2 IS NULL AND date3 IS NOT NULL AND date3 < '20120601' THEN TRUE 
    END 

，並得到了另一個錯誤：An expression of non-boolean type specified in a context where a condition is expected, near 'END'.

Answer 1

這應該工作：

SELECT * 
FROM 
    docs 
WHERE (date1 < '20120601') 
OR (date2 IS NOT NULL AND date2 < '201205601') 
OR (date2 IS NULL AND date3 IS NOT NULL AND date3 < '20120601') 

Answer 2

這個怎麼樣？

SELECT * 
FROM 
    docs 
WHERE date1 < '20120601' 
    AND ISNULL(date2, '20120601') < '20120601' 
    AND ISNULL(date3, '20120601') < '20120601' 

Answer 3

where 
date1 < '20120601' 
    and 
coalesce(date2, date3, '20000101') < '20120601' 

Answer 4

正確的答案是：

SELECT * 
FROM 
    docs 
WHERE 
    date1 < '20120601' AND 
     ((date2 IS NOT NULL AND date3 IS NOT NULL AND date2 < '20120601') OR 
     (date2 IS NOT NULL AND date3 IS NULL AND date2 < '20120601') OR 
     (date2 IS NULL AND date3 IS NOT NULL AND date3 < '20120601'))