Statements

Create statements

Statement objects are created from Connection objects with the createStatement method. For example, assuming a Connection object named conn already exists, the following line of code creates a Statement object for passing SQL statements to the database:

Statement stmt = conn.createStatement();

Specify ResultSet characteristics

The characteristics of ResultSets are associated with the statement that eventually creates them. The Connection.createStatement method allows you to specify these ResultSet characteristics. The following are some examples of valid calls to the createStatement method:

Example: The createStatement method

Note: Read the Code example disclaimer for important legal information.

// The following is new in JDBC 2.0

Statement stmt2 = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATEABLE);

// The following is new in JDBC 3.0

Statement stmt3 = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY, ResultSet.HOLD_CURSOR_OVER_COMMIT);

For more information about these characteristics, see ResultSets.

Process statements

Processing SQL statements with a Statement object is accomplished with the executeQuery(), executeUpdate(), and execute() methods.

Return results from SQL queries

If an SQL query statement returning a ResultSet object is to be processed, the executeQuery() method should be used. You can refer to the example program that uses a Statement object's executeQuery method to obtain a ResultSet.

Note: If an SQL statement processed with executeQuery does not return a ResultSet, an SQLException is thrown.

Return update counts for SQL Statements

If the SQL is known to be a Data Definition Language (DDL) statement or a Data Manipulation Language (DML) statement returning an update count, the executeUpdate() method should be used. The StatementExample program uses a Statement object's executeUpdate method.

Process SQL statements where the expected return is unknown

If the SQL statement type is not known, the execute method should be used. Once this method has been processed, the JDBC driver can tell the application what types of results the SQL statement has generated through API calls. The execute method returns true if the result is at least one ResultSet and false if the return value is an update count. Given this information, applications can use the statement method's getUpdateCount or getResultSet to retrieve the return value from processing the SQL statement. The StatementExecute program uses the execute method on a Statement object. This program expects a parameter to be passed that is an SQL statement. Without looking at the text of the SQL that you provide, the program processes the statement and determines information about what was processed.

Note: Calling the getUpdateCount method when the result is a ResultSet returns -1. Calling the getResultSet method when the result is an update count returns null.

The cancel method

The methods of the native JDBC driver are synchronized to prevent two threads running against the same object from corrupting the object. An exception is the cancel method. The cancel method can be used by one thread to stop a long running SQL statement on another thread for the same object. The native JDBC driver cannot force the thread to stop doing work; it can only request that it stop whatever task it was doing. For this reason, it still takes time for a cancelled statement to stop. The cancel method can be used to halt runaway SQL queries on the system.