当查询在php myadmin中工作时，JDBC抛出语法错误

Question

I am working on java website using jdbc for mysql. Here is my simple function to fetch data from sql,

@Override
    public List fetchMusic(String _uname, String _chnl_name) throws SQLException {

        String sql = "SELECT * FROM `channel_songs` WHERE `uid` = " +
                     " (SELECT `id` FROM `user` WHERE BINARY `uname` = ?)"+
                     " AND `chnl_id` = (SELECT `id` FROM `channel` WHERE BINARY `chnl_name` = ?);";

        Connection conn = dataSource.getConnection();

        PreparedStatement ps = conn.prepareStatement(sql);

        ps.setString(1, _uname);
        ps.setString(2, _chnl_name);

        List<Map<String, Object>> musicListsByChnl = jdbcTemplate.queryForList(String.valueOf(ps));


        return musicListsByChnl;

    }

So, when I am running this, I am getting an error which says,

org.springframework.jdbc.BadSqlGrammarException: StatementCallback; bad SQL grammar [com.mysql.jdbc.JDBC4PreparedStatement@3a4eb50a: SELECT * FROM `channel_songs`]; nested exception is com.mysql.jdbc.exceptions.jdbc4.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 'com.mysql.jdbc.JDBC4PreparedStatement@3a4eb50a: SELECT * FROM `channel_songs`' at line 1

So, I don't know what is wrong or where it is. When I am trying this query on phpmyadmin, it is working properly and returning the data. So can anyone help me here?

Thanx in advance. ;)

Answer 1

You are using the prepared statement wrong... The PreparedStatement is not simply a "convenient" device to build fully escaped SQL strings. The result of String.valueOf(ps) is not actually defined to be a valid SQL command at all. You get ps.toString() , whose value should be used for debugging only. From the exception you gave:

check the manual that corresponds to your MySQL server version for the right syntax to use near 'com.mysql.jdbc.JDBC4PreparedStatement@3a4eb50a: SELECT * FROM channel_songs ' at line 1

You are supposed to do something like this:

@Override
public List fetchMusic(String _uname, String _chnl_name) throws SQLException {

    String sql = "SELECT * FROM `channel_songs` WHERE `uid` = " +
                 " (SELECT `id` FROM `user` WHERE BINARY `uname` = ?)"+
                 " AND `chnl_id` = (SELECT `id` FROM `channel` WHERE BINARY `chnl_name` = ?);";

    Connection conn = dataSource.getConnection();

    PreparedStatement ps = conn.prepareStatement(sql);

    ps.setString(1, _uname);
    ps.setString(2, _chnl_name);

    // This is, where your original code falls apart....
    // List<Map<String, Object>> musicListsByChnl = jdbcTemplate.queryForList(String.valueOf(ps));


    List<Map<String,Object>> answer = new ArrayList<>();

    try (ResultSet rs = ps.executeQuery()) {

        while (rs.next()) {

            // read a single row of the result set using the
            // getters of the `rs` instance (rs.getString(...),
            // rs.getInt(...), ...)
        }
    }



    return musicListsByChnl;

}

If you do not want to write the boiler plate stuff (and as you already seem to have a jdbcTemplate at hand): spring's JdbcTemplate has a lot more convenience methods, which deal with assigning query parameters and the like. Just find the one closest to your needs.