CODEWITHSUNDEEP
mysqlsqldatabaseaggregate-functions
xavier
xavier

Reputation: 19

How to join tables with aggregate functions in MYSQL query?

I have two tables from the database and I want to get the last status of each id. Tried adding the INNER JOIN claus but no avail. These are what my data looks like:

Table: employee

id   name   department
-------------------------
1    A       X
2    B       Y
3    C       Z

Table: timelog

id   time       status    count
-------------------------------
1    08:51       IN       1
3    09:00       OUT      2
2    09:00       IN       3
2    18:00       OUT      4
1    18:05       OUT      5

Currently, this is the query that I use but need to get the name of each employee.

SELECT 
     *
FROM timelog
WHERE timelog.count
IN   (SELECT MAX(timelog.count)
      FROM timelog
      GROUP BY timelog.id) 
ORDER BY clock.id;

Current output:

id   time       status
-------------------------------
1    18:05      OUT
2    18:00      OUT
3    09:00      OUT

This is the output I want to achieve:

id   name      time       status
-------------------------------
1    A         18:05      OUT
2    B         18:00      OUT
3    C         09:00      OUT

Is it possible to add JOIN to the above query? If no, what would be the workaround? Any help would be greatly appreciated. TIA.

Upvotes: 1

Views: 44

Answers (2)

Gordon Linoff
Gordon Linoff

Reputation: 1269693

Use a correlated subquery to get the last record for each id in timelog:

SELECT e.*, tl.*
FROM employee e JOIN
     timelog tl
     ON e.id = tl.id
WHERE tl.count = (SELECT MAX(tl2.count)
                  FROM timelog tl2
                  WHERE tl2.id = tl.id
                 ) ;

Note that your version of the query is not correct. The subquery returns the maximum count for each id. However, the outer query might match a different id to the count in the subquery. The correlation clause fixes this problem.

Upvotes: 1

GMB
GMB

Reputation: 222442

You can join the tables and use a correlated subquery for filtering:

select 
    e.id,
    e.name,
    t.time,
    t.status
from employee e
inner join timelog t on t.id = e.id
where t.count = (
    select max(count)
    from timelog t1
    where t1.id = t.id
)

Upvotes: 1

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