${ew.customSqlSegment} 会直接在前面添加 where
 @Select(select * from a ${ew.customSqlSegment})
 List<a> getA(@Param(Constants.WRAPPER)QueryWrapper queryWrapper)
${ew.sqlSegment} 就只有条件语句
 @Select(select * from a where ${ew.sqlSegment})
 List<a> getA(@Param(Constants.WRAPPER)QueryWrapper queryWrapper)
${ew.sqlSelect} 就是 queryWrapper.select(****) 你所定义需要查询的字段
 @Select(select ${ew.sqlSelect} from a )
 List<a> getA(@Param(Constants.WRAPPER)QueryWrapper queryWrapper)










