获取给定 ID 的最新行

在下面的表格中，我如何只获得基于 signin列的 最近的一次争吵和 id=1，而不是全部3行？

+----+---------------------+---------+
| id | signin              | signout |
+----+---------------------+---------+
|  1 | 2011-12-12 09:27:24 | NULL    |
|  1 | 2011-12-13 09:27:31 | NULL    |
|  1 | 2011-12-14 09:27:34 | NULL    |
|  2 | 2011-12-14 09:28:21 | NULL    |
+----+---------------------+---------+
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最佳答案

Use the aggregate MAX(signin) grouped by id. This will list the most recent signin for each id.

SELECT
id,
MAX(signin) AS most_recent_signin
FROM tbl
GROUP BY id

To get the whole single record, perform an INNER JOIN against a subquery which returns only the MAX(signin) per id.

SELECT
tbl.id,
signin,
signout
FROM tbl
INNER JOIN (
SELECT id, MAX(signin) AS maxsign FROM tbl GROUP BY id
) ms ON tbl.id = ms.id AND signin = maxsign
WHERE tbl.id=1
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SELECT *
FROM   tbl
WHERE  id = 1
ORDER  BY signin DESC
LIMIT  1;

The obvious index would be on (id), or a multicolumn index on (id, signin DESC).

Conveniently for the case, MySQL sorts NULL values last in descending order. That's what you typically want if there can be NULL values: the row with the latest not-null signin.

To get NULL values first:

ORDER BY signin IS NOT NULL, signin DESC

You may want to append more expressions to ORDER BY to get a deterministic pick from (potentially) multiple rows with NULL.
The same applies without NULL if signin is not defined UNIQUE.

Related:

The SQL standard does not explicitly define a default sort order for NULL values. The behavior varies quite a bit across different RDBMS. See:

But there are the NULLS FIRST / NULLS LAST clauses defined in the SQL standard and supported by most major RDBMS, but not by MySQL. See:

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Select [insert your fields here]
from tablename
where signin = (select max(signin) from tablename where ID = 1)
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Building on @xQbert's answer's, you can avoid the subquery AND make it generic enough to filter by any ID

SELECT id, signin, signout
FROM dTable
INNER JOIN(
SELECT id, MAX(signin) AS signin
FROM dTable
GROUP BY id
) AS t1 USING(id, signin)
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SELECT * FROM (SELECT * FROM tb1 ORDER BY signin DESC) GROUP BY id;
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I had a similar problem. I needed to get the last version of page content translation, in other words - to get that specific record which has highest number in version column. So I select all records ordered by version and then take the first row from result (by using LIMIT clause).

SELECT *
FROM `page_contents_translations`
ORDER BY version DESC
LIMIT 1
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Simple Way To Achieve

I know it's an old question You can also do something like 

SELECT * FROM Table WHERE id=1 ORDER BY signin DESC

In above, query the first record will be the most recent record.

For only one record you can use something like 

SELECT top(1) * FROM Table WHERE id=1 ORDER BY signin DESC

Above query will only return one latest record.

Cheers!


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