摘要： 以NULL做where条件过滤时应该写 IS NULL;SELECT * FROM pet WHERE death IS NULL; SELECT * FROM pet WHERE death IS NOT NULL; 注意别加引号。 阅读全文

摘要： 求和命令 mysql> select SUM(price) from order where create_time>'2016-03-12';+------------+| SUM(price) |+------------+| 37.40 |+------------+1 row in set 阅读全文