Java Coding Question And Answers

Getting Particular Rows from a Table

This example retrieves all rows from a table called ''mytable'' whose column COL_A equals ``Patrick Chan''. A row in ''mytable'' consists of a string, integer, and floating point number.

try {
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM mytable WHERE COL_A = 'Patrick Chan'");
rs.next();
String s = rs.getString("COL_A");
int i = rs.getInt("COL_B");
float f = rs.getFloat("COL_C");
process(s, i, f);
} catch (SQLException e) {}

Updating a Row of Data in a Table

This example updates a row in a table called ``mytable''. In particular, for all rows whose column COL_B equals 123, column COL_A is set to ''John Doe''.

try {
Statement stmt = connection.createStatement();
int numUpdated = stmt.executeUpdate(
"UPDATE mytable SET COL_A = 'John Doe' WHERE COL_B = 123");
connection.close();
} catch (SQLException e) {}

Using a Prepared Statement

A prepared statement should be used in cases where a particular SQL statement is used frequently. The prepared statement is more expensive to set up but executes faster than a statement. This example demonstrates a prepared statement for getting all rows from a table called ''mytable'' whose column COL_A equals ''Patrick Chan''. This example also demonstrates a prepared statement for updating data in the table. In particular, for all rows whose column COL_B equals 123, column COL_A is set to ''John Doe''.
try {
// Retrieving rows from the database.
PreparedStatement stmt = connection.prepareStatement("SELECT * FROM mytable WHERE COL_A = ?");
int colunm = 1;
stmt.setString(colunm, "Patrick Chan");
ResultSet rs = stmt.executeQuery();
// Updating the database.
stmt = connection.prepareStatement("UPDATE mytable SET COL_A = ? WHERE COL_B = ?");

colunm = 1;
stmt.setString(colunm, "John Doe");
colunm = 2;
stmt.setInt(colunm, 123);
int numUpdated = stmt.executeUpdate();
} catch (SQLException e) {}