特定列 - 将数据类型nvarchar转换为bigint时出错

Question

这是T-SQL的一部分。我遇到了以下错误。任何人都可以指导我。问题是因为值列是 nvarchar 数据类型

SELECT RuleID, SourceID, DataFileID, ChildCount, DP_State 
FROM        
(SELECT DP_State.RuleID, CAST(DP_State.SourceID AS VARCHAR(20)) AS SourceID, CAST(DP_State.DataFileID AS VARCHAR(20)) AS DataFileID, ChildCount, DP_State
FROM (
        SELECT  RuleID ,
                RuleResultID ,
                CASE WHEN ISNUMERIC(ISNULL([ResultValue], 0)) = 1 THEN                      
                CAST(ISNULL([Value], 0) AS BIGINT)
ELSE
                    -1
                END AS ChildCount,

我收到错误：

Answer 1

如果您使用的是SQL Server 2012或更高版本，请尝试此操作

SELECT RuleID,
    SourceID,
    DataFileID,
    ChildCount,
    DP_State
FROM (
    SELECT DP_State.RuleID,
        CAST(DP_State.SourceID AS VARCHAR(20)) AS SourceID,
        CAST(DP_State.DataFileID AS VARCHAR(20)) AS DataFileID,
        ChildCount,
        DP_State
    FROM (
        SELECT RuleID,
            RuleResultID,
            CASE 
                WHEN TRY_CONVERT(INT, ISNULL([ResultValue],0)) IS NOT NULL
                    THEN CAST(ISNULL([Value], 0) AS BIGINT)
                ELSE - 1
                END AS ChildCount,
        )
    )

Answer 2

您首先在[value]中对0进行ISNULL()检查，然后隐式转换为整数。只有在那之后你才会转换为整数，而是尝试以下方法：

对字符串进行评估：

CAST(ISNULL([Value], '0') AS BIGINT)

或首先转换为整数：

ISNULL(CAST([Value] AS BIGINT), 0)