Oracle: Order by Union returning ORA-00933: SQL command not properly ended

Question

I have an issue with using Oracle's union and order by clauses together.

I have two complex queries (with sub queries in them) having an order by clause for each of them. I need to union the output of both and return the result. When I run it, I am getting the error ORA-00933: SQL command not properly ended.

But it works when I comment out the order by clauses in both of them.

To test this, I created a simple query as simple as shown below

select * from employee where employee_id=2 order by name
union
select * from employee where employee_id=3 order by name;

Even this gave the same error when ran with order by clauses but runs well when I commentout the order by clauses.

I tried searching forums, but I could not get solution for the exact problem. I found one at ORACLE Query with ORDER BY and UNION but As my queries are already too complecated because of subqueries and joins between too many tables, I dont want to implement this.

Can someone help me on fixing the root cause of the issue.

Answer 1

try this code:

select  e1.name name /* e1.* */
  from employee e1
 where employee_id = 2
union
select 
  e2.name name /* e2.* */
  from employee e2
 where employee_id = 3
 order by name;

if you want to order the result of first query then to order the result the second query so you can do like this:

select 1 query, e1.name name /* e1.* */
  from employee e1
 where employee_id = 2
union
select 
 2 query, e2.name name /* e2.* */
  from employee e2
 where employee_id = 3
 order by query, name;

Answer 2

You can have only one ORDER BY when combining multiple queries, on the last statement. The ORDER BY clause acts on the entire set.

See the Oracle Documentation:

You cannot specify the order_by_clause in the subquery of these operators.

Answer 3

If you want order by in each query you must wrap it in other select as a subquery:

select * from (select * from employee where employee_id=2 order by name)
union
select * from (select * from employee where employee_id=3 order by name);