SQL问题 - Java / Web 开发

Java code:

conn = ds.getConnection();
String SQL = "select * from book where id = ?";
PreparedStatement pstm = conn.prepareStatement(SQL);
pstm.setString(1, id);

System.out.println("id:" + id);
System.out.println(SQL);

ResultSet rs = pstm.executeQuery(SQL);



错误信息如下，就是找不到，直接把问号改成1，就可以。传进来的id也没问题啊，可以显示在控制台。用的WebLogic10
Java code:

id:2
select * from book where Id = ?
com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?' at line 1
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:930)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2864)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1567)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1659)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3112)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3041)
at com.mysql.jdbc.Statement.executeQuery(Statement.java:1160)
at weblogic.jdbc.wrapper.Statement.executeQuery(Statement.java:479)
at beans.BookDAO.getBookById(BookDAO.java:83)