從字符串轉換日期和/或時間時轉換失敗

Question

我收到此錯誤：當我嘗試在 SQL 服務器 2008 R2 中運行以下查詢Conversion failed when converting date and/or time from character string ：

    DECLARE @Time datetime = N'7/13/2011'
    DECLARE @str as varchar(100) = '2011_07_13_DM_VT_I2_Data'
    DECLARE @TestTime datetime =  cast(replace (left (left(@str, len(@str) - len('_data')), 10), '_', '') as datetime)
    DECLARE @r int = datediff(d, @TestTime, @Time)

    SELECT t.name FROM
    (
    SELECT 
         name
    FROM 
        sysobjects 
    WHERE 
        (type = 'U') AND ((name LIKE '%[_]I2[_]Data') or (name LIKE '%[_]R4[_]Data') or (name LIKE '%[_]R8[_]Data'))
    ) t

    WHERE
        datediff(DAY, cast(replace (left (left(t.name, len(t.name) - len('_data')), 10), '_', '') as datetime), @Time) <= 1

    ORDER BY 
        cast(replace (left (left(t.name, len(t.name) - len('_data')), 10), '_', '') as datetime) desc

如果我注釋掉WHERE datediff(DAY, cast(replace (left (left(t.name, len(t.name) - len('_data')), 10), '_', '') as datetime), @Time) <= 1這個查詢運行良好WHERE datediff(DAY, cast(replace (left (left(t.name, len(t.name) - len('_data')), 10), '_', '') as datetime), @Time) <= 1 ，那么我想知道這是否是cast function 的問題。 但是t表將具有像'2011_07_13_DM_VT_I2_Data'這樣的表名，您可以在@TestTime中看到強制cast function 可以正常使用這種格式。 我不知道WHERE條件有什么問題。

感謝您的任何幫助。

Answer 1

您需要將查詢分成兩部分，因為看起來查詢優化器已決定應用外部查詢中的 where 子句，然后才從子查詢中的 sysobjects 中過濾掉行。

你可以試試這樣的。

DECLARE @Time datetime = N'7/13/2011'
DECLARE @str as varchar(100) = '2011_07_13_DM_VT_I2_Data'
DECLARE @TestTime datetime =  cast(replace (left (left(@str, len(@str) - len('_data')), 10), '_', '') as datetime)
DECLARE @r int = datediff(d, @TestTime, @Time)

SELECT name INTO #TMP
FROM 
    sysobjects 
WHERE 
    (type = 'U') AND ((name LIKE '%[_]I2[_]Data') or (name LIKE '%[_]R4[_]Data') or (name LIKE '%[_]R8[_]Data'))

SELECT *
FROM #TMP as t
WHERE
    datediff(DAY, cast(replace (left (left(t.name, len(t.name) - len('_data')), 10), '_', '') as datetime), @Time) <= 1

ORDER BY 
    cast(replace (left (left(t.name, len(t.name) - len('_data')), 10), '_', '') as datetime) desc

DROP TABLE #TMP