Question

我在WHERE子句中遇到CASE语句问题。在我的查询中，我想获得日期之前的行。日期检查3列。 date1不是NULL，所以我不需要进行NULL检查，但是日期date2和date3可以为NULL，所以我想检查空值并相应地检查日期条件。我尝试了两种方法，但无法弄清楚如何正确地做到这一点。你能帮我吗？

查询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

第一次出现时出现错误：Incorrect syntax near '<'.

我将查询修改为：

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

又出现了另一个错误：An expression of non-boolean type specified in a context where a condition is expected, near 'END'.

Answer 1

这应该有效：

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

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

Answer 3

这个怎么样？

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

Answer 4

正确的答案是：

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'))

在哪里使用CASE和空检查

4 个答案: