MySQL MIN / MAX returns the correct value but not related record information

Question

I am really stuck with this. I clearly do not understand the MIN / MAX concept.

I am trying to get the last row from the group work_type and work_id.

If I change the value from MIN to MAX, it will change the returned timestamp, but will never output status information from this record.

Example:

"SELECT 
    CONCAT(work_type, work_id) AS condition_id, 
    status,
    MIN(created_timestamp) as latest
  FROM conditions
  GROUP BY condition_id"

With MIN, I get:

    Array
    (
        [0] => Array
            (
                [condition_id] => cutouts00002
                [status] => bad
                [latest] => 2011-02-21 15:20:27
            )

        [1] => Array
            (
                [condition_id] => paintings00002
                [status] => damagez
                [latest] => 2011-02-21 14:43:35
            )

    )

With MAX, I get:

Array
(
    [0] => Array
        (
            [condition_id] => cutouts00002
            [status] => bad
            [latest] => 2011-02-21 15:22:20
        )

    [1] => Array
        (
            [condition_id] => paintings00002
            [status] => damagez
            [latest] => 2011-02-21 14:43:41
        )

)

But the fact is that the status in the line with the last timestamp is “not damaged”, but it never returns the line corresponding to MAX (current_timestamp), it only ever returns the line “damagez”.

Any help is appreciated.

Thank.

Answer 1

lax MySQL, GROUP BY. , MIN MAX ONE , :

SELECT 
    CONCAT(work_type, work_id) AS condition_id, 
    status,
    MIN(created_timestamp) as earliest,
    MAX(created_timestamp) as latest
  FROM conditions
  GROUP BY condition_id

, . ( GROUP BY) .

SELECT X.condition_id, C.status, X.earliest
FROM (
  SELECT 
    CONCAT(work_type, work_id) AS condition_id, 
    status,
    MIN(created_timestamp) as earliest
  FROM conditions
  GROUP BY condition_id
) X JOIN conditions C
  on CONCAT(c.work_type, c.work_id) = X.condition_id
  and c.created_timestamp = X.earliest

created_timestamp,

SELECT X.condition_id, Max(C.status) status, X.earliest
FROM (
  SELECT 
    CONCAT(work_type, work_id) AS condition_id, 
    status,
    MIN(created_timestamp) as earliest
  FROM conditions
  GROUP BY condition_id
) X JOIN conditions C
  on CONCAT(c.work_type, c.work_id) = X.condition_id
  and c.created_timestamp = X.earliest
GROUP BY X.condition_id, X.earliest

Answer 2

- .

- T-SQL, , .

SELECT 
    CONCAT(c.work_type, c.work_id) as condition_id, 
    c.status, 
    c.created_timestamp as latest
FROM conditions c
JOIN (SELECT work_type, work_id, max(current_timestamp) as latest GROUP BY work_type, work_id) c2 
    ON c.work_type = c2.work_type
    AND c.work_id = c2.work_id
    AND c.created_timestampe = c2.latest

Answer 3

WHERE, .

SELECT 
    CONCAT(work_type, work_id) AS condition_id, 
    status,
    created_timestamp as latest
FROM
    conditions
WHERE
    created_timestamp = (
        SELECT
            MIN(conditions2.created_timestamp)
        FROM
            conditions AS conditions2
        WHERE
            conditions2.condition_id = conditions.condition_id
    )
GROUP BY
    condition_id

In addition, if the first query must contain any additional join or where clause, they can be repeated in a subquery.

SELECT 
    CONCAT(work_type, work_id) AS condition_id, 
    status,
    created_timestamp as latest
FROM
    conditions
    INNER JOIN some_table on condition.id = some_table.condition_id
WHERE
    some_table.some_column > 50 AND 
    created_timestamp = (
        SELECT
            MIN(conditions2.created_timestamp)
        FROM
            conditions AS conditions2
            INNER JOIN some_table AS some_table2 on condition2.id = some_table2.condition_id
        WHERE
            some_table.some_column > 50 AND 
            conditions2.condition_id = conditions.condition_id
    )
GROUP BY
    condition_id