In the table below, how do I get just the most recent row with id=1 based on the signin column, and not all 3 rows?
+----+---------------------+---------+ | 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 | +----+---------------------+---------+ 7 Answers
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 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:
- SQL how to make null values come last when sorting ascending
- Sort by column ASC, but NULL values first?
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) Select [insert your fields here] from tablename where signin = (select max(signin) from tablename where ID = 1) SELECT * FROM (SELECT * FROM tb1 ORDER BY signin DESC) GROUP BY id; 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 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!
