SQL 表中的最后一个 id 值。数据库服务器
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Last id value in a table. SQL Server
提问by cMinor
Is there a way to know the last nthid field of a table, without scanning it completely? (just go to the end of table and get id value)
有没有办法知道表的最后一个nthid 字段，而无需完全扫描它？（只需转到表的末尾并获取 id 值）
table
id fieldvalue
1 2323
2 4645
3 556
... ...
100000000 1232
So for example here n = 100000000100 Million
因此，例如这里n = 1000000001 亿
--------------EDIT-----So which one of the queries proposed would be more efficient?
--------------编辑-----那么提出的哪一个查询会更有效？
回答by rayman86
SELECT MAX(id) FROM <tablename>
回答by rsbarro
Assuming ID is the IDENTITY for the table, you could use SELECT IDENT_CURRENT('TABLE NAME').
假设 ID 是表的 IDENTITY，您可以使用SELECT IDENT_CURRENT('TABLE NAME').
See herefor more info.
请参阅此处了解更多信息。
One thing to note about this approach:If you have INSERTs that fail but increment the IDENTITY counter, then you will get back a result that is higher than the result returned by SELECT MAX(id) FROM <tablename>
关于这种方法需要注意的一件事：如果您的插入失败但增加了 IDENTITY 计数器，那么您将返回一个高于返回结果的结果SELECT MAX(id) FROM <tablename>
回答by kosmo
You can also use system tables to get all last values from all identity columns in system:
您还可以使用系统表从系统中的所有标识列中获取所有最后一个值：
select
OBJECT_NAME(object_id) + '.' + name as col_name
, last_value
from
sys.identity_columns
order by last_value desc
回答by vooxo
In case when table1rows are inserted first, and then rows to table2which depend on ids from the table1, you can use SELECT:
如果table1首先插入行，然后插入table2依赖于 id 的行，则table1可以使用SELECT：
INSERT INTO `table2` (`some_id`, `some_value`)
VALUES ((SELECT some_id
FROM `table1`
WHERE `other_key_1` = 'xxx'
AND `other_key_2` = 'yyy'),
'some value abc abc 123 123 ...');
Of course, this can work only if there are other identifiers that can uniquely identify rows from table1
当然，这只有在有其他标识符可以唯一标识行的情况下才有效 table1
回答by Md Shahriar
Select Ident_Current('Your Table Name') gives the last Id of your table.
Select Ident_Current('Your Table Name') 给出表的最后一个 ID。
回答by Michael Dillon
First of all, you want to access the table in DESCENDING order by ID.
首先，您要按 ID 以 DESCENDING 顺序访问表。
Then you would select the TOP N records.
然后您将选择前 N 条记录。
At this point, you want the last record of the set which hopefully is obvious. Assuming that the id field is indexed, this would at most retrieve the last N records of the table and most likely would end up being optimized into a single record fetch.
在这一点上，您需要该集合的最后一条记录，希望这是显而易见的。假设 id 字段被索引，这最多将检索表的最后 N 条记录，并且很可能最终会被优化为单个记录提取。
