SQL in Java. Cannot receive the result set

Question

I hope that you can correct me if my syntax is wrong. I could check on Google only if the SELECT...WHERE clause is correct.

I want to retrieve the student_id for using it in another query, but seems that all I get from this is a "0".

in java file:

rst = stmt.executeQuery("SELECT student_id FROM students WHERE name= 'to_delete'");
sid = rst.getInt("student_id");

to_delete is a String which this java file receives as a parameter to the method which must return student_id. It really contains the correct string(I checked it).

Table "students" contains the fileds: student_id, name, year. I need to have returned the student_id for the name "to_delete".

I have no errors/exceptions, just that when I display the result, I see id: 0 no matter what name I type. Maybe rst.getString("column_name") is correct only for executeUpdate(...)?

Thank you in advance!

Nathan Hughes · Accepted Answer · 2012-07-02 14:12:52Z

3

Call next() on the resultset before you try to get anything out of it. You iterate through the ResultSet by calling the next method every time you want to read a row. When next returns false you're done.

Here's the API documentation for the next method:

boolean next() throws SQLException

Moves the cursor froward one row from its current position. A ResultSet cursor is initially positioned before the first row; the first call to the method next makes the first row the current row; the second call makes the second row the current row, and so on.

When a call to the next method returns false, the cursor is positioned after the last row. Any invocation of a ResultSet method which requires a current row will result in a SQLException being thrown. If the result set type is TYPE_FORWARD_ONLY, it is vendor specified whether their JDBC driver implementation will return false or throw an SQLException on a subsequent call to next.

If an input stream is open for the current row, a call to the method next will implicitly close it. A ResultSet object's warning chain is cleared when a new row is read.

Returns: true if the new current row is valid; false if there are no more rows Throws: SQLException - if a database access error occurs or this method is called on a closed result set

edited Jul 2, 2012 at 14:12

answered Jul 2, 2012 at 14:02

Nathan Hughes

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3 Comments

dj_segfault Over a year ago

Just to expand on that a little, the value returned from the query is a result set, which you can think of as a collection. You have to iterate through the collection one row at a time. So next() will get a row, and then you can get column values from the row.

Nathan Hughes Over a year ago

@dj_segfault: except keeping in mind the resultSet isn't really a collection, it's more like a wrapper around a database cursor.

dj_segfault Over a year ago

Yeah, I realize what I wrote could be taken that way. It's better to think of it as an iterator than a collection.

TechGuy · Accepted Answer · 2012-07-02 14:05:34Z

0

Yes.the problem is you should call next() before you try to get from it.Otherwise you did not get any error but No results.

answered Jul 2, 2012 at 14:05

TechGuy

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