关于Mysql查询查询无法正常工作

Question

我对一个视图运行一个非常简单的查询，它使用一个值，并且不能与其他值一起工作。我试图从不同的索引值视图中选择行只指数1.5返回的结果

以下是查看表的样本

我有这种说法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

select * from easylens where `index`=1.5 

我得到

+---+----+------+----+-----+-----+-----+-------+--------+ 
|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

select * from easylens where `index`=1.6 

我得到

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

Answer 1

浮动的危险（与不确定的精度和小数）

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 | 
+----+------+--------+------+-------+-------+-------+---------+----------+ 

Answer 2

尝试投

SELECT * FROM easylens WHERE CAST(`index` as DECIMAL) = CAST(1.6 as DECIMAL);