错误地更新查询结果 [英] Update query resulting wrongly

问题描述

我有一个名为company_emp的表.在该表中，我有6个与员工相关的列:

I have table called company_emp. In that table I have 6 columns related to employees:

1. empid
2. ename
3. dob
4. doj，...

我还有一个名为bday的表.因为我只有两栏；温和和多宝.

I have another table called bday. In that I have only 2 columns; empid and dob.

我有这个查询:

select empid, dob 
from company_emp 
where dob like '01/05/2011'

它显示了一些雇员列表.

It shows some list of employees.

以同样的方式查询表bday，其中列出了一些员工.

In the same way I have queried with table bday it listed some employees.

现在，我要更新日期为'01/05/2011'的雇员的company_emp表.

Now I want to update the company_emp table for employees who have date '01/05/2011'.

我尝试过这样的查询:

update company_name a
 set dob = (select dob from bday b 
            where b.empid=a.empid 
              and to_char(a.dob,'dd/mm/yyyy') = '01/05/2011'}

然后该行中的所有记录变为空.如何解决此查询?

Then all the records in that row becoming null. How can I fix this query?

推荐答案

您正在更新company_name/emp表中的每一行.

You're updating every row in the company_name/emp table.

您可以使用相关子查询来解决该问题，以确保该行存在，或者通过在bday.empid上放置主键或唯一键并进行查询来更有效地进行查询:

You can fix that with a correlated subquery to make sure the row exists, or more efficiently by placing a primary or unique key on bday.empid and querying:

update (
  select c.dob to_dob,
         d.dob from_dob
  from   company_emp c join dob d on (c.empid = d.empid)
  where  d.dob = date '2011-05-01')
set to_dob = from_dob

语法未经测试.

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