mysql查询为什么不准确

Question

SELECT * from se_contractcust_rel where REL_ID=160816071200000009;
返回结果
rel_id                                       contract_id                            cust_id
160816071200000009 160816071200000008 100000271039
160816071200000015 160816071200000014 100000271039
结果多出来一条，虽然找到问题，rel_id类型是varchar,查询条件不标准，但是为什么会出现这种情况，mysql中是什么机制导致的

Answer 1

rel_id类型是varchar，你的查询条件应当加引号， where REL_ID='160816071200000009';

Answer 2

他们会转化成浮点数是相等的
mysql> select '160816071200000009'+0.0,'160816071200000015'+0.0;
+--------------------------+--------------------------+
| '160816071200000009'+0.0 | '160816071200000015'+0.0 |
+--------------------------+--------------------------+
|           1.608160712e17 |           1.608160712e17 |
+--------------------------+--------------------------+
1 row in set (0.00 sec)mysql>