偶尔会发生:"将数据类型nvarchar转换为float时出错"

Question

这是我的SQL查询:

SELECT (CAST(CAST([rssi1] AS float) AS INT))*-1, CONVERT(VARCHAR(10), [date], 110)
FROM history
WHERE id IN
(
    SELECT TOP 8 id
    FROM history
    WHERE ([siteName] = 'CAL00022') 
    ORDER BY id DESC
)
ORDER BY date ASC

大多数时候,它工作正常.有时,我收到此错误:

Server Error in '/' Application.
Error converting data type nvarchar to float.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.Data.SqlClient.SqlException: Error converting data type nvarchar to float.

表是这样的:

Answer 1

当你不相信你所选择的引擎中的实数处理时,你会将它们存储在nvarchars中,这太可怕了!我已经找回足够的1.000000000001来表示同情,但也不太喜欢这个解决方案.

根据约翰的回答,识别您的无效记录是必要的,但无论如何您可能无法亲自对此做任何事情.您提供的是SELECT语句,有时会失败,因此,我解决了这个失败.

在尝试转换之前检查rssi1的值是否为数字可以避免您有时得到的错误.您可以排除rssi1不是数字的那些记录:

SELECT
  (CAST(CAST([rssi1] AS float) AS INT))*-1,
  CONVERT(VARCHAR(10), [date], 110)
FROM history
WHERE id IN
(
    SELECT TOP 8 id
    FROM history
    WHERE ([siteName] = 'CAL00022') 
    ORDER BY id DESC
)
AND ISNUMERIC([rssi1]) = 1
ORDER BY date ASC

或按原样呈现(每个都有它自己的限制):

SELECT
  CASE WHEN ISNUMERIC([rssi1]) = 1 THEN CAST((CAST(CAST([rssi1] as float) as int))*-1 as nvarchar) ELSE [rssi1] /* Or choose a value to default to */ END, 
  CONVERT(VARCHAR(10), [date], 110)
FROM history
WHERE id IN
(
    SELECT TOP 8 id
    FROM history
    WHERE ([siteName] = 'CAL00022') 
    ORDER BY id DESC
)
ORDER BY date ASC