查询字段对应=null的值(特殊)
isNull
QueryWrapper<User>queryWrapper = newQueryWrapper<>();
queryWrapper
.isNull("creat_time")
.ge("count", 12)
.isNotNull("QQ");
int result = userMapper.delete(queryWrapper);
between
QueryWrapper<User>queryWrapper = newQueryWrapper<>();
queryWrapper.between("amount", 20, 30);
Integer count = userMapper.selectCount(queryWrapper); //返回数据数量