Java Reference
In-Depth Information
only, similar to reading data from an input stream. Once the cursor is positioned over
a row, we can use one of following methods to retrieve data from a specific column in
the current row:
intVal = resultSet.getInt("name of int field");
lngVal = resultSet.getLong("name of bigint field");
strVal = resultSet.getString("name of varchar field");
dblVal = resultSet.getDouble("name of double field");
fltVal = resultSet.getFloat("name of float field");
The program in Display 19.13 can run once the database is created with the
program given in Display 19.12. It retrieves and outputs all rows in the table by
executing a SELECT query with no WHERE clause and then retrieves and outputs only
those rows with any author_id greater than 1. Invoke the close( ) method to free
resources when finished using a ResultSet object.
Finally, we can change the contents of an existing row using the SQL UPDATE
command. In the UPDATE command, we specify the table, field(s) to change, new
value(s), and a WHERE clause to indicate which rows should be changed. If the WHERE
clause is omitted, then every row in the table is updated. The syntax is described in the
box “Common SQL Statements.” Display 19.14 shows an example where the URL field
is changed to a new value entered by the user. The URL field is only changed for the row
that matches the author_id entered by the user.
Display 19.13
Retrieving Rows with the SELECT Statement (part 1 of 3)
The database must be created (Display 19.12)
before running the program.
1 import java.sql.Connection ;
2 import java.sql.DriverManager;
3 import java.sql.ResultSet;
4 import java.sql.SQLException;
5 import java.sql.Statement;
6 public class ReadDB
7 {
8 private static final String driver =
"org.apache.derby.jdbc.EmbeddedDriver";
9 private static final String protocol = "jdbc:derby:";
10 /*
11 Outputs the author, ID, and URL of the current
12 author in the ResultSet
13 */
14 public static void displayNameRow(ResultSet rs) throws SQLException
15 {
16 int id = rs.getInt("author_id");
17 String author = rs.getString("author");
18 String url = rs.getString("url");
The accessor methods
throw the checked exception
SQLException.
(continued)
 
Search WWH ::




Custom Search