WHAT ARE SUBQUERIES IN ORACLE?
Subqueries in Oracle mean nested queries. In an easy term, the subquery can be identified as a query inside the main query. This article will be covering the following topics on Subqueries:
SELECT Column_name FROM Table_Name
where column_Name Operator(subquery)...;
we need to find maximum Roll_No in the Stu table:
One way to do that is by writing a simple query:
Select Max(Roll_No) from Stu ;
Either way to do it is by using the subquery method. For instance, now I need to find details of the student who have the greatest Roll_No:
Select * from Stu
where Roll_No =(Select Max(Roll_No) from Stu )
The above query shows a clear example of the subquery.
Now the question arises, How the above query works?
Well, firstly the inner query or the nested query:
Select Max(Roll_No) from Stu;
executes and results as:
Moving ahead, the main query will now follow the logic as:
select * from Stu
and will display results as: