我有一个小的mysql表（MySQL版本5.6.23）：

+-----------+-----------------+------+-----+---------+----------------+
| Field     | Type            | Null | Key | Default | Extra          |
+-----------+-----------------+------+-----+---------+----------------+
| id        | int(6) unsigned | NO   | PRI | NULL    | auto_increment |
| dividends | float(8,6)      | YES  |     | NULL    |                |
+-----------+-----------------+------+-----+---------+----------------+

我的where子句遵循row-subqueries语法。
如果我做：

SELECT id, dividends FROM test  
  where  (id,dividends) >= (660,0.5);

或者

SELECT id, dividends FROM test 
  where  (id,dividends) >= (660,CAST(0.5 AS DECIMAL(8,6)));

我得到这个结果：

+-----+-----------+
| id  | dividends |
+-----+-----------+
| 660 |  0.500000 |
| 661 |  0.470000 |
| 662 |  0.470000 |
| 663 |  0.470000 |
| 664 |  2.580000 |
| 665 |  2.581000 |
...

在我看来，没有考虑股息> = 0.5。为什么？