mysql - Mysql View 查询无法正常工作

Question

我在一个 View 上运行一个非常简单的查询，它适用于一个值，不适用于所有其他值。我正在尝试从 View 中选择具有不同索引值的行，仅索引 1.5 返回结果

以下是 View 表的示例

我有这个View easylens

select * from easylens

+---+----+------+----+-----+-----+-----+-------+--------+
|id |type|design|name|brand|index|color|coating|material|
+---+----+------+----+-----+-----+-----+-------+--------+
| 1 | sv |aase  |nel |hoya |  1.5|292  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 2 | sv |base  |tel |zeri |  1.5|293  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 3 | sv |case  |fel |essi |  1.5|294  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 4 | sv |dase  |gel |hoya |  1.6|293  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 5 | sv |fase  |rel |essi |  1.6|293  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 6 | sv |gase  |mel |hoya |  1.6|292  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+

当我运行时

select * from easylens where `index`=1.5

我明白

+---+----+------+----+-----+-----+-----+-------+--------+
|id |type|design|name|brand|index|color|coating|material|
+---+----+------+----+-----+-----+-----+-------+--------+
| 1 | sv |aase  |nel |hoya |  1.5|292  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 2 | sv |base  |tel |zeri |  1.5|293  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+
| 3 | sv |case  |fel |essi |  1.5|294  |ar     |plastic |
+---+----+------+----+-----+-----+-----+-------+--------+

但是当我运行时

select * from easylens where `index`=1.6

我明白

MySQL returned an empty result set (i.e. zero rows). (Query took 0.0002 sec)

Answer 1

float 的危险(未定义的精度和小数位数)

SELECT * FROM easylens WHERE `index` = 1.6000000238418578;
+----+------+--------+------+-------+-------+-------+---------+----------+
| id | type | design | name | brand | index | color | coating | material |
+----+------+--------+------+-------+-------+-------+---------+----------+
|  4 | sv   | dase   | gel  | hoya  |   1.6 |   293 | ar      | plastic  |
|  5 | sv   | fase   | rel  | essi  |   1.6 |   293 | ar      | plastic  |
|  6 | sv   | gase   | mel  | hoya  |   1.6 |   292 | ar      | plastic  |
+----+------+--------+------+-------+-------+-------+---------+----------+