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Retrieving the tuples in a result set

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• Retrieving (iterating through) the tuples in a ResultSet
  • Retrieving the the next tuple from the result set:

    rset.next() (1) Retreives the next tuple in result set object rset (2) Method returns null if no more tuples in rset

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  • Program structure to retrieve all tuples in the result set:

    while ( rset.next() != null ) { // Use rset object to access the attribute values // in the current tuple in the result set rset.getString(1); rset.getInt(2); etc, etc }

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• Methods used to get attribute values in the current tuple
  • Commonly used methods for retrieving an attribute value in the current tuple rset:

    rset.getString(index): return the attribute at position index as a String rset.getInt(index): return the attribute at position index as an int type rset.getLong(index): return the attribute at position index as a long type rset.getFloat(index): return the attribute at position index as a float type rset.getDouble(index): return the attribute at position index as a double type

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  • How to use these methods:

    ResultSet rset; // Result set (cursor) rset = SQLstatement.executeQuery("some SQL-query"); while ( rset.next () ) { String stringVar = rset.getString(index); int intVar = rset.getInt(index); long longVar = rset.getLong(index); float floatVar = rset.getFloat(index); double doubleVar = rset.getDouble(index); (there are many more other flavor of get() that I omitted....) }

    Example: print the first 8 attributes in every tuple

    while ( rset.next () ) // rset will loop through every tuple in result { System.out.println ( rset.getString(1) + " " // Get 1st attribute value in tuple + rset.getString(2) + " " // Get 2nd attribute value in tuple + rset.getString(3) + " " // Get 3rd attribute value in tuple + rset.getString(4) + " " // And so on + rset.getString(5) + " " + rset.getString(6) + " " + rset.getString(7) + " " + rset.getString(8) ); }

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  • Note:

    You need meta information to know the data type of a particular attribute We will discuss how to use meta information in JDBC later.

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• Program structure used to retrieve all tuples in result set object rset
  • How to use the result set rset:

    // Assume the we have executed a query and // rset contains the result set /* ================================================= Retrive all tuples in the result set ================================================= */ while ( rset.next () ) // Get next tuple in result set rset { /* ====================================================== Print the retrieved attributes from the current tuple ====================================================== */ System.out.println ( rset.getString(1) + " " // Get 1st attribute value in tuple + rset.getString(2) + " " // Get 2nd attribute value in tuple + rset.getString(3) + " " // Get 3rd attribute value in tuple + rset.getString(4) + " " // And so on + rset.getString(5) + " " + rset.getString(6) + " " + rset.getString(7) + " " + rset.getString(8) // I "blindly" retrieve 8 attribute values... ); } /* ============================================================= After you finish using rset, you should "destroy" the object ============================================================= */ rset.close(); // Destroy the result set object // It's "OK" if you don't do this // Then Java will then clean it up later // through its garbage collection mechanism...

    Note:

    We have not (yet) learn how to find the number of attributes in the result set rset That's why I "blindly" retrieved 8 attribute values in the above example.... (We will learn how to use the meta data to find the number of attributes later)