CODEWITHSUNDEEP
javasqloracle-databaseresultset
Yevgeniy Klymenko
Yevgeniy Klymenko

Reputation: 3

Possibility of SQL query to return a result set that has more than one column with the same name

From oracle doc http://docs.oracle.com/javase/1.5.0/docs/guide/jdbc/getstart/resultset.html

In some cases, it is possible for an SQL query to return a result set that has more than one column with the same name. If a column name is used as the parameter to a getXXX method, getXXX will return the value of the first matching column name.

Anybody knows about "some cases"?

Upvotes: 0

Views: 258

Answers (3)

Chris Travers
Chris Travers

Reputation: 26454

Here's a common example:

SELECT * FROM table1 JOIN table2 ON table1.table1Id = table2.table1Id;

Here you know table1 and table2 have a column named table1Id, and it is guaranteed to have the same value. However if you have a self-join:

SELECT * FROM employee e JOIN employee m ON e.manager_id = m.id;

Now you have a problem and, probably, your result set will not make as much sense.

Upvotes: 0

Markus Benko
Markus Benko

Reputation: 1507

Imagine two tables defined as

  • Authors: AuthorId, FirstName, LastName, Title...
  • Books: BookId, Title, ISBN, AuthorId...

where one would want to list books with author information using the following SQL

SELECT *
FROM Books
JOIN Authors USING (AuthorId)

Now you have two unrelated title columns in the ResultSet, one being the title of the book and one being the (e.g. academic) title of the author.

Upvotes: 0

Serg
Serg

Reputation: 22811

The simplest case is

select 1 as A, 2 as A from dual

much the same way someone may (unwillingly) create equal aliases in a complex query.

Upvotes: 2

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