MySQL行子查询比较问题

Question

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);

要么

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,股息> = 0.5没有被考虑在内.为什么？

Answer 1

你正在使用行构造函数.MySQL将它们视为与表的行完全相同.因此WHERE (id,dividends) >= (660,0.5)有效地做到:

1. ORDER BY id,dividends;

2. 找到符合(660,0.5)该顺序的点;

3. 仅过滤那些等于或大于排序中该点的记录.

因此,它是一样的WHERE (id=660 AND dividends>=0.5) OR id>660.

看起来好像你真正希望表达的逻辑是WHERE id>=660 AND dividends>=0.5.