Order of the output

Question

I have a query
Eg: select id,name from user
where user.id in ('a7','a6','a3',....); --- ID's are in different order not, in ascending or descending
the output of the above query is something like
id name
a3 a3_name
a7 a7_name
a6 a6_name
But I would like the output to be in the order input was given inside
a7 a7_name
a6 a6_name
a3 a3_name
How do we do this?

Answer 1

user651347 wrote:
I had a list given with 300 users and neither in ASC or DESC order
so we need to order this the way it was given or in the select ... in (); statementOk. Did you mathematical "set" theory at school? Familiar with Venn diagrams?
If you are, let's look at two sets of values.... (1,2,3,4) and (4,3,2,1)....
As a Venn diagram you'd end up drawing those two sets as:-
Set A                                             Set B
#                    #   2  #                     #
#                    #  1     #                     #
#                    #   4    #                     #
#                    #   3  #                     #
            #######               #######They are identical sets and there is no order to them.
You can even do this in SQL, to see if there is a difference in the two sets...
SQL> create or replace type myset as table of number;
  2  /
Type created.
SQL> select myset(1,2,3,4) multiset except myset(4,3,2,1) as diff from dual;
DIFF
MYSET()As you can see, it doesn't matter what order the elements of the set are specified in. As a SET, they are considered identical. The order of the elements when specifying the sets makes no difference.
So, in your query, you can pass your elements to you IN operator in any order you like... but those elements are a SET of data... they have no order, except in the way you read them. Oracle see's no order to them, and cannot consider there to be an order to them.
Therefore, if you need an order to the elements, using a SET of data is not the right approach as it doesn't contain an order. You would need to specify a set of data that contains information about the order, and you'd usually do that by inserting the elements into a table (Global Temporary Table perhaps?) with some additional column containing details of the order, and then in your query, you would use the ORDER BY clause to order on that additional ordering information.
The only way to guarantee the order of output from an SQL statement is to specify an ORDER BY clause. ^1^
^1 There are a few exceptions such as hierarchical queries or data generating queries such as those with recursive subquery factoring or model clauses if used in certain ways^