简单的动态 TSQL 查询语法

2022-01-16 00:00:00 sql tsql sql-server sql-server-2008-r2 dynamic-sql

这可能是一个简单的答案，但我已经盯着它太久了......

This may be an easy answer but I've been staring at it for too long...

我有以下查询，它将存储过程输入参数作为变量名并计算该表中的记录.我想将动态语句 (@toStartStr) 的结果检索到变量 (@toStart) 中.

I have the following query that takes a stored procedure input parameter as a variable name and counts the records in that table. I'd like to retrieve the results of the dynamic statement (@toStartStr) into a variable (@toStart). 

-- @tempTableName = SProc input parameter
DECLARE @toStartStr nvarchar(150);
DECLARE @toStart int;
SET @toStartStr = 'SELECT @toStart = COUNT(ID) FROM ' + @tempTableName;
EXEC(@toStartStr);

现在，一个错误提示 @toStart 不能与字符串 SELECT 连接，但这是我想要的要点.谁能看到我做错了什么?或者提出替代方案?仅供参考 SQL 2008 R2.谢谢.

Right now, an error suggests that @toStart cannot be concatenated with the string SELECT, but this is the gist of what I want. Can anyone see what I'm doing wrong? Or suggest an alternative? FYI SQL 2008 R2. Thanks.

推荐答案

DECLARE @sql NVARCHAR(255);

DECLARE @toStart INT;

SET @sql = N'SELECT @toStart = COUNT(ID) FROM ' + QUOTENAME(@tempTableName);

EXEC sp_executesql @sql, N'@toStart INT OUTPUT', @toStart OUTPUT;

PRINT @toStart;

但是，如果您可以忽略当前正在进行的事务(并且您使用的是 SQL Server 2005 或更高版本 - 请在提问时指定版本！).

However there is a much easier and more efficient way to do this, if you're okay with ignoring current in-flight transactions (and you're using SQL Server 2005 or better - please specify the version when asking questions!).

DECLARE @toStart INT;

SELECT @toStart = SUM(rows) 
  FROM sys.partitions
  WHERE [object_id] = OBJECT_ID(@tempTableName)
  AND index_id IN (0,1);

PRINT @toStart;

为了完整起见，这里是 SQL Server 2000 的解决方案，它也不需要任何特殊权限(只需连接和公众成员):

Just for completeness, here is a solution for SQL Server 2000, which also doesn't require any special privileges (just connect and member of public):

DECLARE @toStart INT;

SELECT @toStart = [rows] 
  FROM sysindexes
  WHERE id = OBJECT_ID(@tempTableName)
  AND indid IN (0,1);

PRINT @toStart;

也就是说，如果您使用计数来确定下一个 ID 可能是什么，或者类似的东西，我认为您的方法是错误的，因为可以删除行并且如果它是标识列值由于回滚，可以跳过.

That said, if you're using a count to determine what the next ID might be, or something like that, I think you're approaching this the wrong way, since rows can be deleted and if it's an identity column values can be skipped due to rollbacks.

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