sql - 偶尔发生 : "Error converting data type nvarchar to float"

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.

表格是这样的:

Answer 1

当您非常不信任所选引擎中对实数的处理以致将它们存储在 nvarchars 中时，真是太糟糕了!我已经检索到足够的 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，但您可能无法亲自对此采取任何行动。您提供的是有时会失败的 SELECT 语句，因此，我解决了该失败问题。

在尝试转换之前检查 rssi1 的值是否为数字可以避免您有时遇到的错误。您可以排除那些 rssi1 不是数字的记录:

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