Get Last non-null cell in a row mysql - mysql

Question

I have a table in following structure:
id performance_id employee_comments manager_comments
1 23 NULL Well done.
2 46 NULL Improve Speed
3 46 Trying to improve NULL
4 46 NULL Put more effort
In above structure, at a time, only one comments exist, either employee_comments or manager_comments, not both simultaneously.
I want to fetch last non-empty employee comments and manager_comments in a single row.
I need mysql query to display output as:
performance_id employee_comments manager_comments
23 NULL Well done.
46 Trying to improve Put more effort

Answer 1

You can get the largest id for each of the employee comments and manager comments, per performance_id this way:
SELECT performance_id,
MAX(CASE WHEN employee_comments IS NOT NULL THEN id END) AS emp_id,
MAX(CASE WHEN manager_comments IS NOT NULL THEN id END) AS mgr_id
FROM MyTable
GROUP BY performance_id
The above only returns one row per performance_id, with two id numbers. These are the "last" entries, as determined by greater id numbers.
Output:
+----------------+--------+--------+
| performance_id | emp_id | mgr_id |
+----------------+--------+--------+
| 23 | NULL | 1 |
| 46 | 3 | 4 |
+----------------+--------+--------+
With that result, you can join it back to the table to retrieve other columns:
SELECT t.performance_id,
t.employee_comments,
t.manager_comments
FROM (
SELECT performance_id,
MAX(CASE WHEN employee_comments IS NOT NULL THEN id END) AS emp_id,
MAX(CASE WHEN manager_comments IS NOT NULL THEN id END) AS mgr_id
FROM MyTable
GROUP BY performance_id
) AS x
JOIN MyTable AS t ON t.id IN (emp_id, mgr_id)
Output:
+----------------+-------------------+------------------+
| performance_id | employee_comments | manager_comments |
+----------------+-------------------+------------------+
| 23 | NULL | Well done. |
| 46 | Trying to improve | NULL |
| 46 | NULL | Put more effort |
+----------------+-------------------+------------------+
The above return up to two rows per performance_id. You can use another GROUP BY to force them onto one row:
SELECT t.performance_id,
MAX(t.employee_comments) AS employee_comments,
MAX(t.manager_comments) AS manager_comments
FROM (
SELECT performance_id,
MAX(CASE WHEN employee_comments IS NOT NULL THEN id END) AS emp_id,
MAX(CASE WHEN manager_comments IS NOT NULL THEN id END) AS mgr_id
FROM MyTable
GROUP BY performance_id
) AS x
JOIN MyTable AS t ON t.id IN (emp_id, mgr_id)
GROUP BY performance_id
Output:
+----------------+-------------------+------------------+
| performance_id | employee_comments | manager_comments |
+----------------+-------------------+------------------+
| 23 | NULL | Well done. |
| 46 | Trying to improve | Put more effort |
+----------------+-------------------+------------------+

Answer 2

try this query
SELECT t.id,t.performance_id,t2.employee_comments,t3.manager_comments FROM test1 t join test1 t2 on t2.employee_comments IS NOT NULL and t.manager_comments IS NULL
join test1 t3 on t3.manager_comments IS NOT NULL and t.id < t3.id
group by t.performance_id

Answer 3

This can be done by a nested query in MySQL. We will have to do a union and group by performance_id
SELECT performance_id ,MAX(employee_comments)
employee_comments,MAX(manager_comments) manager_comments
FROM(
SELECT performance_id,employee_comments,manager_comments FROM MyTable
WHERE id IN (SELECT * FROM
(SELECT id FROM MyTable WHERE manager_comments IS NOT NULL ORDER BY id DESC)AS t)
UNION
SELECT performance_id,employee_comments,manager_comments FROM MyTable
WHERE id IN (SELECT * FROM
(SELECT id FROM MyTable WHERE employee_comments IS NOT NULL ORDER BY id DESC) AS p)) g GROUP BY performance_id;
The above query should work for fetching the last non-empty employee comments and manager_comments
I have tried and tested it...