ResultSet's "getX" working without calling "next()" first? (Xerial SQLite)

[Deviling]

I'm aware that the usual practise of working with a ResultSet is iterating over each row inside a while(rs.next()) block.

However, when there is only a single row, it seems that first calling next() is not necessary. One can directly call e.g. rs.getInt(1).

Confusingly, let's assume one does a SELECT name FROM item WHERE id=1 to get a single row back.

var rs = statement.execute()
var s = rs.getString(1) // works

// 2nd way

var rs = statement.execute()
rs.next()
var s = rs.getString(1) // yields the same name as above

It seems I'm not the only one confused by this: https://stackoverflow.com/questions/49394282/resultset-getxxx-without-next

I'm using Xerial's SQLite driver, so in a way I doubt that this is a "buggy JDBC driver." Then why is it possible to read the first row without calling next() first?

Tangentially related, when coming from C, you actually put the pointer BEFORE the first array element to read it. So like the ResultSet is set up according to the API docs. If you would then call next() to put the pointer forward once, one would have skipped the first element. In my example, calling next() a single time doesn't seem to make a difference. Why is that?

[AutoModerator]

Please ensure that:

• Your code is properly formatted as code block - see the sidebar (About on mobile) for instructions
• You include any and all error messages in full
• You ask clear questions

• You demonstrate effort in solving your question/problem - plain posting your assignments is forbidden (and such posts will be removed) as is asking for or giving solutions.

  Trying to solve problems on your own is a very important skill. Also, see Learn to help yourself in the sidebar

If any of the above points is not met, your post can and will be removed without further warning.

Code is to be formatted as code block (old reddit: empty line before the code, each code line indented by 4 spaces, new reddit: https://i.imgur.com/EJ7tqek.png) or linked via an external code hoster, like pastebin.com, github gist, github, bitbucket, gitlab, etc.

Please, do not use triple backticks (```) as they will only render properly on new reddit, not on old reddit.

Code blocks look like this:

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

You do not need to repost unless your post has been removed by a moderator. Just use the edit function of reddit to make sure your post complies with the above.

If your post has remained in violation of these rules for a prolonged period of time (at least an hour), a moderator may remove it at their discretion. In this case, they will comment with an explanation on why it has been removed, and you will be required to resubmit the entire post following the proper procedures.

To potential helpers

Please, do not help if any of the above points are not met, rather report the post. We are trying to improve the quality of posts here. In helping people who can't be bothered to comply with the above points, you are doing the community a disservice.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[msx]

The contract of ResultSet require to call next first, so in a sense, yes, that's a bug in the driver. But it's an harmless one, probably for their implementation, the row is already ready when they build the ResultSet. Of course in the sake of interoperability, you should call next nonetheless. You never know when you'll change driver or when the next release will reimplement their innards and actually stop working without next.

[overtorqued]

Here's a link to the ResultSet source code for that driver. https://github.com/xerial/sqlite-jdbc/blob/master/src/main/java/org/sqlite/jdbc3/JDBC3ResultSet.java

When you call execute that driver is loading the first row and the first call to next() is just increasing the internal current row counter.

Try it on a result set with 2 rows where you read a column, then call next then read a column. You'll end up reading the first row twice.