How can I UPDATE the result of a SELECT statement? - php

Question

I have a table like this:
// notifications
+----+--------------+------+---------+------------+
| id | event | seen | id_user | time_stamp |
+----+--------------+------+---------+------------+
| 1 | vote | 1 | 123 | 1464174617 |
| 2 | comment | 1 | 456 | 1464174664 |
| 3 | vote | 1 | 123 | 1464174725 |
| 4 | answer | 1 | 123 | 1464174813 |
| 5 | comment | NULL | 456 | 1464174928 |
| 6 | comment | 1 | 123 | 1464175114 |
| 7 | vote | NULL | 456 | 1464175317 |
| 8 | answer | NULL | 123 | 1464175279 |
| 9 | vote | NULL | 123 | 1464176618 |
+----+--------------+------+---------+------------+
And here is my query:
(SELECT id, event, seen, time_stamp
FROM notifications n
WHERE id_user = :id AND seen IS NULL
)UNION
(SELECT id, event, seen, time_stamp
FROM notification n
WHERE id_user = :id AND seen IS NOT NULL
LIMIT 2
)UNION
(SELECT id, event, seen, time_stamp
FROM notifications n
WHERE id_user = :id
ORDER BY (seen IS NULL) desc, time_stamp desc
LIMIT 15
)
ORDER BY (seen IS NULL) desc, time_stamp desc;
Now I'm trying to update matched rows from query above and set seen = 1, Something like this:
UPDATE notifications SET seen = 1 WHERE /* the result of query above */
How can I do that?
Note: I also use PHP and PDO to execute that SELECT query (If it is important to know)
$stm = $db->prepare(" (SELECT id, ... ");
$stm->execute( /* passing some variables */);
$stm->fetchAll(PDO::FETCH_ASSOC);

Answer 1

seen can only be 1 or null. In that case, most of what you are getting from that UNION query is irrelevant. It seems to me that the end result of the update you're trying to do will be:
UPDATE notifications SET seen = 1 WHERE id_user = :id AND seen IS NULL
Anything else will be updating something that's already 1 to 1.

Answer 2

I think you can use where in clause .. but in this case you need ond the id
UPDATE notifications SET seen = 1 WHERE id in (
(SELECT id
FROM notifications n
WHERE id_user = :id AND seen IS NULL
)UNION
(SELECT id
FROM notification n
WHERE id_user = :id AND seen IS NOT NULL
LIMIT 2
)UNION
(SELECT id
FROM notifications n
WHERE id_user = :id
ORDER BY (seen IS NULL) desc, time_stamp desc
LIMIT 15
))

Answer 3

If you want to do this in MySQL, use JOIN:
update notifications n join
(select id
from ((SELECT id, event, seen, time_stamp
FROM notifications n
WHERE id_user = :id AND seen IS NULL
) UNION
(SELECT id, event, seen, time_stamp
FROM notification n
WHERE id_user = :id AND seen IS NOT NULL
LIMIT 2
) UNION
(SELECT id, event, seen, time_stamp
FROM notifications n
WHERE id_user = :id
ORDER BY (seen IS NULL) desc, time_stamp desc
LIMIT 15
)) n
) nids
on n.id = nids.id
set seen = 1;

Answer 4

You can slightly modify your query to use as subquery for update statement:
UPDATE notifications SET seen = 1 WHERE id in (
(SELECT id
FROM notifications n
WHERE id_user = :id AND seen IS NULL
)UNION
(SELECT id
FROM notification n
WHERE id_user = :id AND seen IS NOT NULL
LIMIT 2
)UNION
(SELECT id
FROM notifications n
WHERE id_user = :id
ORDER BY (seen IS NULL) desc, time_stamp desc
LIMIT 15
)
)

Answer 5

I assume you have retrieved all applicable ID's into your application. All you need to do is then is
UPDATE notifications
SET seen = 1
WHERE id IN (?,?,?)
where the ? are replaced by the id values.