Mysql Union Query Record result emptys column - mysql

Question

I have a union query to get a Max date record from two tables
SELECT
id,
MAX(mx) AS max_date,
`assigned_user_id`
FROM (SELECT
id,
MAX(date_due) AS mx,
`assigned_user_id`
FROM tasks
WHERE `deleted` = 0
AND `parent_id` = 'aa6f0330-7a17-572f-94b5-4a5db1a1201f'
AND `parent_type` = 'Accounts'
AND date_due >= CURDATE() UNION SELECT
id,
MAX(date_start) AS mx,
`assigned_user_id`
FROM calls
WHERE `deleted` = 0
AND `account_id` = 'aa6f0330-7a17-572f-94b5-4a5db1a1201f'
AND date_start >= CURDATE()) s
this would look into both calls and Tasks and get me the Futuristic Call or a Task, but when i run this and i have a Futuristic Call and task is older, i get NULL in id and assigned_user_id columns. How do i fetch the whole info for the MAX date record.
When i Run individual Queries, i get null for first one while a record in the second one.

Answer 1

Perhaps I'm misreading the problem, or I'm missing something - in which case, write me a comment to let me know, and I can delete this post altogether.
But, the way I understand what you've written, you want to:
Get the single record in tasks with the given parent_id and parent_type and where date_due >= CURDATE() which has the latest date_due value.
Get that same type of record from the calls table (using date_start instead of date_due).
Of those two records, find the one record with the later date value. Select the id, the date (as max_date), and the assigned_user_id from that record.
Your query (and sub-queries) could just order by descending date and fetch only the first record.
I'm thinking something like this...
SELECT id,
mx AS max_date,
`assigned_user_id`
FROM (
SELECT id,
date_due as mx,
`assigned_user_id`
FROM tasks
WHERE `deleted` = 0
AND `parent_id` = 'aa6f0330-7a17-572f-94b5-4a5db1a1201f'
AND `parent_type` = 'Accounts'
AND date_due >= CURDATE()
ORDER BY date_due DESC
LIMIT 1
UNION
SELECT id,
date_start as mx,
`assigned_user_id`
FROM calls
WHERE `deleted` = 0
AND `account_id` = 'aa6f0330-7a17-572f-94b5-4a5db1a1201f'
AND date_start >= CURDATE()
ORDER BY date_start DESC
LIMIT 1
)
ORDER BY max_date DESC
LIMIT 1

Answer 2

Use UNION ALL. To allow duplicate values, use the ALL keyword with UNION.

Answer 3

Select Max(max_date) from
(SELECT
id,
MAX(mx) AS max_date,
assigned_user_id
FROM
(SELECT
id,
MAX(date_due) AS mx,
assigned_user_id
FROM tasks
WHERE deleted = 0
AND parent_id = 'aa6f0330-7a17-572f-94b5-4a5db1a1201f'
AND parent_type = 'Accounts'
AND date_due >= CURDATE() group by id UNION SELECT
id,
MAX(date_start) AS mx,
assigned_user_id
FROM calls
WHERE deleted = 0
AND account_id = 'aa6f0330-7a17-572f-94b5-4a5db1a1201f'
AND date_start >= CURDATE()) s group by id)
as temp