conditional select statement in oracle

Question

I have two tables called order and public holiday as following:

Order Table:

OrderId      OrderDate
---------------------------
    1        10 Mar 2017
         


        

Answer 1

Changed the table name of order to ordero as order is a Keyword

 select ordero.orderid, ordero.orderdate, holiday.holidaydate,case when holiday.holidaydate is not null then 'Public Holiday'
 else to_char(ordero.orderdate,'Day') end "Day" 
 from ordero left outer join holiday on ordero.orderdate=holiday.holidaydate;

Answer 2

Two things to remeber:

1. ORDER is a keyword, so please use another table name
2. CASE statement should be ended with END not with END AS

Possible solution:

SELECT O.OrderId,
  O.OrderDate,
  CASE
    WHEN H.HolidayDate IS NOT NULL
    THEN 'Public holiday'
    ELSE TO_CHAR(O.OrderDate, 'Day')
  END DAY
FROM ORDER_TABLE O
LEFT JOIN HOLIDAY_TABLE H
ON H.HolidayDate=O.OrderDate;

Answer 3

You can use an outer join like this:

SELECT OrderId,
       OrderDate, 
       case when holidaydate is not null then  'Public holiday' 
             else to_char(OrderDate, 'Day') end as DAY
from orders
     left outer join holidays
        on OrderDate = holiday_date ;

If the dates match holidaydate is not null so the CASE clause displays your desired string otherwise it displays the day of the orderdate .

---

order is a reserved word. Presumably your real table has a different name, to avoid the ora-00903 error. I have used orders in my example, so you will need to edit my code to match your table name(s).