Question

我有一个以下要求，但我不知道如何编写Oracle SQL查询以根据给定条件获取数据。

要求：

人员表

Name       created_date   updated_date
-------    -----------    ------------
Alex       11-oct-2018     
John       10-oct-2018    11-oct-2018

我想基于UI上给出的起始和日期来获取记录名称，created_date或updated_date作为last_modified_date，并且如果updated_date不为null，它应该搜索fromdate和todate之间的updated_date，例如updateddate。如果updated_date为null，则应在fromdate和todate之间搜索created_date之类的内容，例如created_date。

我这样尝试过，存在编译问题，我不怎么写

select name,
       case when update_date is null then created_date else updated_date as last_modified_date 
from Person 
where case when updated_date is null 
           then trunc(created_date) between fromdate and todate 
           else trunc(updated_date) between fromdate and todate.'

Answer 1

像这样吗？

select name, nvl(update_date,created_date) as last_modified_date
from Person 
where nvl(update_date,created_date) between fromdate and todate;

Answer 2

您在where子句上编写正确的sql语法时确实犯了错误，如下所示

    select name, 
           case when update_date is null 
           then created_date else 
           updated_date end as last_modified_date 
    from Person
    where case when updated_date 
    is null then trunc(created_date)
      else 
    trunc(updated_date) end
    between fromdate and todate

通过使用COALESCE函数，您可以进行相同的比较

select name,COALESCE(update_date,created_date)
from Person
where COALESCE(update_date,created_date) between fromdate and todate

您的错误区域

    case when updated_date 
    is null then trunc(created_date) between fromdate and todate --here between is wrong sql syntax (condition)
   else 
    trunc(updated_date) between fromdate and todate --(same thing you did for else)

Answer 3

使用：

在[条件]然后[return_expr] ELSE [else_expr]结束时的情况

Select name, 
       CASE WHEN update_date IS NULL
            THEN created_date
            ELSE updated_date END AS last_modified_date
  FROM Person
 WHERE CASE WHEN updated_date IS NULL
            THEN TRUNC(created_date)
            ELSE TRUNC(updated_date) END BETWEEN fromdate AND todate;

或仅用于oracle：

NVL（[expr1]，[expr2]）

Select name, 
       NVL(update_date, created_date) AS last_modified_date
  FROM Person
 WHERE NVL(updated_date, created_date) BETWEEN fromdate AND todate;

WHERE子句中的CASE或IF条件满足以下要求

3 个答案: