Update query resulting wrongly

Question

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

1. empid
2. ename
3. dob
4. doj, ...

Answer 1

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

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

Syntax not tested.