SQL Server删除记录

Question

I have two tables computers , and softwareinstalls .

Computers primary key is computerid, softwareinstalls has three fields (installid, computerid, and lastmodifieddate).

Software installs computerid joined with computers.computerid.

I'm trying to delete all softwareinstalls on a computer that have a last modified date more than 1 day before the max for that computer, so...

software installs table

install  computerid  lastmodifieddate
1        1           01-16-13
2        1           01-16-13
3        1           01-14-13
4        2           01-12-13
5        2           01-10-13

would delete records 3 and 5. what would be the query in sql server?

Answer 1

You can join on delete statements. Use LEFT JOIN on this.

DELETE  a
FROM    softwareinstalls a
        LEFT JOIN
        (
            SELECT computerID, max(lastmodifieddate) max_date
            FROM softwareinstalls
            GROUP BY computerID
        ) b ON a.computerID = b.computerID AND
                a.lastmodifieddate = b.max_date
WHERE   b.computerID IS NULL

• SQLFiddle Demo

For better performance, add an index on columns computerID and lastmodifieddate .