Slide 12.8: Executing a query

Executing a Query

A simple database transaction uses only one of the three execution methods in the Statement Interface:

public ResultSet executeQuery( String sql ) throws SQLException
It executes an SQL statement that returns a single ResultSet object. This method should be used for any SQL calls that expect to return data from the database. For example,

  ResultSet rset = stmt.executeQuery(
    "SELECT ename FROM emp WHERE eid='7772413'" );

public int executeUpdate( String sql ) throws SQLException
It executes an SQL INSERT, UPDATE, or DELETE statement. In addition, SQL statements that return nothing, such as SQL DDL statements, can be executed. This method returns the number of affected rows. For example,
stmt.executeUpdate ( "insert into customers values ( 'Pokemon', '123456789', 0 )" );
public boolean execute( String sql ) throws SQLException
It is for situations in which you do not know whether the SQL being executed is a query or update. For example,
```
  try {
    stmt.execute( "drop table people" );
    stmt.execute( "drop type PERSON FORCE" );
    stmt.execute( "drop type ADDRESS FORCE" );
  }
  catch ( SQLException e ) {
    System.out.println( e );
  }
```
^†This usually happens when the application is executing dynamically created SQL statements.

The class SQLException provides information on a database access error or other errors.