SQL select query with multiple conditions issue - mysql

Question

I have a problem with a SQL select query, I can't figure out what it needs to be.
This is what my items table look like:
| id | i_id | last_seen | spot |
----------------------------------------------------
| 1 | ls100 | 2017-03-10 15:30:40 | spot800 |
| 2 | ls100 | 2017-03-10 16:20:15 | spot753 |
| 3 | ls200 | 2017-03-10 16:33:10 | spot800 |
| 4 | ls300 | 2017-03-10 15:30:40 | spot800 |
| 5 | ls300 | 2017-03-10 12:10:30 | spot800 |
| 6 | ls400 | 2017-03-10 10:30:10 | spot800 |
This is what I'm trying to obtain:
| id | i_id | last_seen | spot |
----------------------------------------------------
| 3 | ls200 | 2017-03-10 16:33:10 | spot800 |
| 5 | ls300 | 2017-03-10 12:10:30 | spot800 |
So I need to have the rows where spot= 'spot800', last_seen = MAX(but only if the DateTime is the newest compared to all spots with the samei_id`), and at last the DateTime must be bigger than '2017-03-10 11:00:00'.
This is what I have so far:
SELECT *
FROM items
WHERE spot = 'spot800'
HAVING MAX(`last_seen`)
AND `last_seen` > '2017-03-10 11:00:00'

Answer 1

E.g.:
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,i_id INT NOT NULL
,last_seen DATETIME NOT NULL
,spot INT NOT NULL
);
INSERT INTO my_table VALUES
(1,100,'2017-03-10 15:30:40',800),
(2,100,'2017-03-10 14:20:15',753),
(3,200,'2017-03-10 16:33:10',800),
(4,300,'2017-03-10 15:30:40',800),
(5,300,'2017-03-10 12:10:30',800),
(6,400,'2017-03-10 10:30:10',800);
SELECT [DISTINCT] x.*
FROM my_table x
LEFT
JOIN my_table y
ON y.i_id = x.i_id
AND y.last_seen < x.last_seen
WHERE x.last_seen > '2017-03-10 11:00:00'
AND x.spot = 800
AND y.id IS NULL;
----+------+---------------------+------+
| id | i_id | last_seen | spot |
+----+------+---------------------+------+
| 3 | 200 | 2017-03-10 16:33:10 | 800 |
| 5 | 300 | 2017-03-10 12:10:30 | 800 |
+----+------+---------------------+------+
2 rows in set (0.00 sec)

Answer 2

Use MAX and GROUP BY.
SELECT id, i_id, MAX(last_seen), spot
FROM items
WHERE spot = 'spot800'
AND last_seen > '2017-03-10 11:00:00'
GROUP BY id, i_id, spot

Answer 3

There is several things wrng with your statement.
Firstly, HAVING must be accompanied with a GROUP BY clause, so it's not what you are looking for.
Also, MAX is an aggregate, not a boolean, function. That is, it cannot be used in filters, such as a where clause or a having clause. Also, if it did work, MAX would only return the entry that contains the time as '2017-03-10 16:33:10'. Not what you expected.
Try this instead:
SELECT * FROM items WHERE (spot='spot800' AND last_seen > '2017-03-10 11:00:00');