Is there a way to give a subquery an alias in Oracle 11g SQL?
You can give a query a name or alias with CTE’s (Common Table Expressions) aka WITH clause aka by Oracle as Subquery Factoring:
WITH abc as (select client_ref_id, request from some_table where message_type = 1)select * from abc inner join (select client_ref_id, response from some_table where message_type = 2) defg on abc.client_ref_id = def.client_ref_id;
I don't have an Oracle instance to test with, but what you posted should be valid ANSI-89 JOIN syntax. Here it is in ANSI-92:
SELECT * FROM (SELECT client_ref_id, request FROM SOME_TABLE WHERE message_type = 1) abc JOIN (SELECT client_ref_id, request FROM SOME_TABLE WHERE message_type = 1) defg ON defg.client_ref_id = abc.client_ref_id
Your query should be fine.
An alternative would be:
select abc.client_ref_id, abc.request, def.responsefrom some_table abc, some_table defwhere abc.client_ref_id = def.client_ref_idand abc.message_type = 1and def.message_type = 2;
I wouldn't be surprised if Oracle rewrote the queries so that the plan would be the same anyway.