Behavior of SELECT query using executeUpdate

Question

I have come across a strange behavior while executing a SELECT query using Statement#executeUpdate() by mistake. While the Javadoc clearly states that executeUpdate() throws SQLException if the given SQL statement produces a ResultSet object. But when I'm executing SELECT * from TABLE_NAME, I don't get any exception. Instead I'm getting an return value which is same as the no. of rows selected, if no. is less than or equal to 10. If the no. is more than 10, the return value is always 10.

Connection conn;
Statement stmt;
try {
    conn = getConnection();
    stmt = conn.createStatement();
    int count = stmt.executeUpdate("SELECT * from TABLE_NAME");
    log.info("row count: " + count);
} catch (SQLException e) {
    log.error(e);
    // handle exception
} finally {
    DbUtils.closeQuietly(stmt);
    DbUtils.closeQuietly(conn);
}

I am using Oracle 10g.

Am I missing something here or is it up to the drivers to define their own behavior?

Answer 1

This behaviour is definetely contradicts Statement.executeUpdate API. What's interesting, java.sql.Driver.jdbcCompliant API says "A driver may only report true here if it passes the JDBC compliance tests". I tested oracle.jdbc.OracleDriver.jdbcCompliant - it returns true. I also tested com.mysql.jdbc.Driver.jdbcCompliant - it returns false. But in the same situation as you describe it throws

Exception in thread "main" java.sql.SQLException: Can not issue SELECT via executeUpdate().

It seems that JDBC drivers are unpredictable.

Answer 2

According to the specifications Statement.executeUpdate() method returns the row count for SQL Data Manipulation Language (DML).

UPD: I attempted to make an assumption about the returned result (which is always <=10). It seems, that the oracle statement's implementation returns here a number of a such called premature batch count (according to the decompiled sources OraclePreparedStatement class). This is somehow linked to the update statements. May be this value equals 10 by default.

UPD-2: According to this: Performance Extensions: The premature batch flush count is summed to the return value of the next executeUpdate() or sendBatch() method.