将 Null 值传递给 Dynamic SQL 和 OPENQUERY 的变量

Question

我有一个查询需要将变量值传递到动态 SQL/openquery 查询中。

declare @week int = 14
declare @id varchar(10) = 10

declare @SQL varchar(MAX), @OQWeek varchar(2) = @Week, @OQID varchar(10) = @ID

SET @sql = N'SELECT * FROM OPENQUERY(SERVER1,''SELECT T.SID ,   T.AgentNo , T2.Duration
                                        FROM server1.DB1.Table1 T
                                        inner join server1.DB1.Table2 T2 on t2.SID=f.SID 
                    WHERE Week =' + @OQWeek + ' and  T2.SID= ISNULL(' + @OQID + ',T2.SID) ' + ''')'

exec( @sql)

如果我在@id 变量中输入一个值，它似乎可以正常运行，但是如果我输入 'NULL' 进入它刚刚返回的变量 Commands completed successfully.

当我也使用 COALESCE() 时也是如此。

如何像在直接 SQL 查询中那样 handle/pass 通过空值？ WHERE 子句的正常 SQL 版本通常如下所示 WHERE Week = @OQWeek and T2.SID= ISNULL(@OQID, T2.SID)

Answer 1

如果您的变量之一 @OQWeek 或 @OQID 的值为 NULL，则整个字符串将解析为 NULL，如 'Some String' + NULL = NULL.

处理动态语句之外的NULL。因为如果值为 NULL 则不需要子句，所以当它是时不要包含它。我假设这仅适用于 @OQWeek，因为这是你包裹 ISNULL 的变量：

DECLARE @week int = 14,
        @id varchar(10) = 10

DECLARE @SQL nvarchar(MAX), --This was the wrong data type
        @OQWeek varchar(2)= @Week,
        @OQID varchar(10) = @ID,
        @CRLF nchar(2) = NCHAR(13) + NCHAR(10);

SET @SQL = N'SELECT * FROM OPENQUERY(SERVER1,N''SELECT T.SID, T.AgentNo , T2.Duration' + @CRLF +
           N'                                  FROM server1.DB1.Table1 T' + @CRLF +  --do you really have a database called "Server1" on your instance "Server1"?
           N'                                       INNER JOIN server1.DB1.Table2 T2 on t2.SID=f.SID' + @CRLF + 
           N'                                  WHERE Week = ' + @OQWeek + --Careful, syntax like this is open to injection
           CASE WHEN @OQID IS NOT NULL THEN @CRLF + N'                                    AND T2.SID = ' + @OQID ELSE '' END + ';'');'

--PRINT @SQL; --Your debugging best friend
EXEC sys.sp_executesql @SQL; --Don't use EXEC(@SQL), you can't parametrise it.

将 Null 值传递给 Dynamic SQL 和 OPENQUERY 的变量

Passing Null values into Variable for Dynamic SQL and OPENQUERY

sql

sql-server

openquery