C#ADO.net查询运行缓慢

我有一个.net通过ADO到Sql Server 2012构建和执行的查询。如果ADO执行查询，它会在等待数据库返回时超时，但如果我将其复制并通过SQL Management studio并针对同一数据库执行查询，它将在不到一秒钟的时间内返回

我发现，将ADO生成的查询包装在“将其存储在SQL变量中并使用SP_EXECUTESQL”中，可以使其运行良好且快速。为什么会有区别呢？我没有以任何方式更改查询

这里是它构建和执行的查询之一（我省略了动态构建CommandText设置为的字符串的所有代码）

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这种行为通常是由问题引起的。您可以尝试使用“重新编译”或“针对未知对象进行优化”选项

选项重新编译 为未知优化

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注意不要对

varchar

列使用

nvarchar

参数，因为这会导致隐式强制转换，请注意，我们的应用程序是国际性的，因此我们对所有列都使用nvarchar。在using语句生成字符串之前，我必须创建一个存储过程，以完成大量.NET代码行的工作。字符串是动态构建的，因此每次执行它时，结构都是一致的。插入的数量及其为临时表选择的表都是动态的。将两个实际的查询计划作为XML发布并比较它们（禁用超时以获得较慢的计划）。它们可能会在慢速版本中显示转换警告。不需要这样做。特设SQL能够实现相同级别的性能。只需使用SQL事件探查器捕获计划。有一个XML Showplan事件。或者，捕获查询并在SSMS中重新执行它们。

using(SqlConnection conn = ConnectionStringHelper.GetOpenConnection)
using(SqlCommand cmd = conn.CreateCommand)
{
    cmd.CommandType = CommandType.Text;
    cmd.Parameters.AddWithValue("agencyID", broadcastAgencyID);
    cmd.Parameters.AddWithValue("tableName", mapping.TableName);
    cmd.Parameters.AddWithValue("schemaName", mapping.SchemaName);
    cmd.Parameters.AddWithValue("broadcastEntityMappingID", mapping.BroadcastEntityMappingID);

    cmd.CommandText = @"SET NOCOUNT ON; 
        DECLARE @currentAgencyID NVARCHAR(MAX)
        DECLARE @currentFacilityID NVARCHAR(MAX)

        DECLARE @currentAgencyEntityBroadcastID INT
        SELECT broadcastEntity.AgencyID, broadcastEntity.FacilityID
        INTO #missingBroadcasts
        FROM [Resource].[AgencyFacility] broadcastEntity
        LEFT JOIN(
            SELECT keys.AgencyID, keys.FacilityID
                , record.BroadcastAgencyID
                , record.AgencyEntityBroadcastID
            FROM [Propagation].[AgencyEntityBroadcast] record
            INNER JOIN (
                SELECT AgencyEntityBroadcastID
                    ,[AgencyID], [FacilityID]
                FROM (
                    SELECT AgencyEntityBroadcastID
                        ,ColumnName AS [PropagationColumnName]
                        ,ColumnValue AS [PropagationColumnValue]
                    FROM Propagation.AgencyEntityBroadcastKeys
                    ) Keys
                PIVOT(MAX(PropagationColumnValue) FOR PropagationColumnName IN (
                            [AgencyID], [FacilityID]
                            )) pivoted
                ) keys ON keys.AgencyEntityBroadcastID = record.AgencyEntityBroadcastID
                WHERE record.BroadcastAgencyID = @agencyID
                    AND record.BroadcastEntityMappingID = @broadcastEntityMappingID
            ) keys ON keys.BroadcastAgencyID = broadcastEntity.AgencyID
                AND keys.AgencyID = broadcastEntity.AgencyID
            AND keys.FacilityID = broadcastEntity.FacilityID
        WHERE broadcastEntity.AgencyID = @agencyID
            AND keys.AgencyEntityBroadcastID IS NULL
        DECLARE entity_cursor CURSOR FOR
        SELECT * FROM #missingBroadcasts

        OPEN entity_cursor
        FETCH NEXT FROM entity_cursor
        INTO @currentAgencyID, @currentFacilityID
        WHILE @@FETCH_STATUS = 0
        BEGIN
            INSERT INTO Propagation.AgencyEntityBroadcast(
                BroadcastAgencyID,
                BroadcastEntityMappingID,
                BroadcastTypeID,
                CreatedOn,
                ModifiedOn
            )
            VALUES(
                @agencyID,
                @broadcastEntityMappingID,
                1,
                GETUTCDATE(),
                GETUTCDATE()
            )

            SET @currentAgencyEntityBroadcastID = (SELECT SCOPE_IDENTITY())
            INSERT INTO Propagation.AgencyEntityBroadcastKeys(
                AgencyEntityBroadcastID,
                ColumnName,
                ColumnValue
            ) VALUES (
                @currentAgencyEntityBroadcastID,
                'AgencyID',
                @currentAgencyID
            )
        INSERT INTO Propagation.AgencyEntityBroadcastKeys(
            AgencyEntityBroadcastID,
            ColumnName,
            ColumnValue
        ) VALUES (
            @currentAgencyEntityBroadcastID,
            'FacilityID',
            @currentFacilityID
        )

        FETCH NEXT FROM entity_cursor INTO @currentAgencyID, @currentFacilityID
        END

        CLOSE entity_cursor
        DEALLOCATE entity_cursor

        DROP TABLE #missingBroadcasts

        SET NOCOUNT OFF;";

    cmd.ExecuteNonQuery();
}

....
WHERE broadcastEntity.AgencyID = @agencyID
            AND keys.AgencyEntityBroadcastID IS NULL
OPTION (RECOMPILE)

.....
WHERE broadcastEntity.AgencyID = @agencyID
      AND keys.AgencyEntityBroadcastID IS NULL
OPTION (OPTIMIZE FOR (@agencyID UNKNOWN, @broadcastEntityMappingID UNKNOWN))