### The error may involve defaultParameterMap ### The error occurred while setting parameters

Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Query was empty
; bad SQL grammar []; nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Query was empty]

今天用mybatis+pageHelp时发生这个错误，原因是：

错误代码：

    public PageInfo<Log> getLogPage(Integer pageNum) {
        //设置每页显示数量
        int pageSize = 5;
        PageHelper.startPage(pageNum, pageSize);
        //执行分页查询
        NMRoutingToken token = new NMRoutingToken("LOG_DATA_SOURCE_KEY");
        List<String> tableNameList = logMapper.selectAlltableName();

        NMRoutingToken token1 = new NMRoutingToken("LOG_DATA_SOURCE_KEY");

        List<Log> logList=logMapper.selectAllLog(tableNameList);
        //对获取的数据进行包装
        int navigatePages = 6;
        PageInfo<Log> page = new PageInfo<>(logList, navigatePages);
        return page;
    }    

正确：

    public PageInfo<Log> getLogPage(Integer pageNum) {

        //执行分页查询
        NMRoutingToken token = new NMRoutingToken("LOG_DATA_SOURCE_KEY");
        List<String> tableNameList = logMapper.selectAlltableName();

        NMRoutingToken token1 = new NMRoutingToken("LOG_DATA_SOURCE_KEY");
        //设置每页显示数量
        int pageSize = 5;
        PageHelper.startPage(pageNum, pageSize);
        List<Log> logList=logMapper.selectAllLog(tableNameList);
        //对获取的数据进行包装
        int navigatePages = 6;
        PageInfo<Log> page = new PageInfo<>(logList, navigatePages);
        return page;
    }

pageHelp的页面设置应该在指定的sql前