Select by date doesn't seem to work - mysql

Question

As I am not the world's greatest SQLer, I am working up to something big, step by step.
I have a table:
mysql> describe taps;
+---------------+-----------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------------+-----------+------+-----+-------------------+-------+
| tag_id | int(11) | YES | | NULL | |
| time_stamp | timestamp | NO | | CURRENT_TIMESTAMP | |
| event_id | int(11) | YES | | NULL | |
| event_station | int(11) | YES | | NULL | |
| device_id | text | YES | | NULL | |
| device_type | text | YES | | NULL | |
+---------------+-----------+------+-----+-------------------+-------+
6 rows in set (0.00 sec)
And would like to select all entries for a given date (today, 12th Feb, '17).
I am trying
mysql> select * from taps WHERE (event_id=4)
AND ((time_stamp >= 1486857600000) AND (time_stamp <= 1486944000000));
Empty set, 2 warnings (0.00 sec)
IMPORTANT: I have simplified things, because I want to compare with variables, which have values which I have obtained from another table, which are also of type timestamp.
Hmmm, warnings ....
mysql> SHOW WARNINGS;
+---------+------+----------------------------------------------------------------------------+
| Level | Code | Message |
+---------+------+----------------------------------------------------------------------------+
| Warning | 1292 | Incorrect datetime value: '1486857600000' for column 'time_stamp' at row 1 |
| Warning | 1292 | Incorrect datetime value: '1486944000000' for column 'time_stamp' at row 1 |
+---------+------+----------------------------------------------------------------------------+
2 rows in set (0.00 sec)
So, I tried casting
select * from taps WHERE (event_id=4)
AND ((time_stamp >= CAST(1486857600000 AS DATETIME))
AND (time_stamp <= CAST(1486944000000 AS DATETIME)));
Empty set (0.00 sec)
Which I don't understand, as I am the table does have some entries today.
mysql> select * from taps order by time_stamp limit 3;
+--------+---------------------+----------+---------------+-----------+-------------+
| tag_id | time_stamp | event_id | event_station | device_id | device_type |
+--------+---------------------+----------+---------------+-----------+-------------+
| 44 | 2017-02-12 15:10:25 | NULL | 16 | NULL | NULL |
| 37 | 2017-02-12 15:10:27 | NULL | 14 | NULL | NULL |
| 50 | 2017-02-12 15:10:28 | NULL | 15 | NULL | NULL |
+--------+---------------------+----------+---------------+-----------+-------------+
3 rows in set (0.00 sec)
What am I doing wrongly? And what should my query be?

Answer 1

MySQL has very confusing terminology for date/time stuff (see here). A timestamp is essentially a datetime with a timezone, because the value is stored as UTC, but reported in the local timezone.
This timestamp is not to be confused with a Unix Timestamp, which is just the number of seconds since 1970-01-01 (or in some cases milliseconds).
In your case, try this:
select t.*
from taps t
where event_id = 4 and
time_stamp >= '2017-02-11 07:00:00' and
time_stamp < '2017-02-12 07:00:00';
You could use from_unixtimestamp(). However, people generally find date formats much easier to read.
Note: I changed the last condition to a strict inequality. This gives you 24 hours with no duplication of time, in case something happens at exactly 2017-02-12 07:00:00.

Answer 2

In SQL, literal TIMESTAMP values are normally supplied as strings, in the format 'YYYY-MM-DD HH:MM:SS'. MySQL does allow some latitude in the actual format. More recent versions of MySQL allow for fractional seconds. See the MySQL Reference Manual for a more complete description.
https://dev.mysql.com/doc/refman/5.6/en/datetime.html
As an example, MySQL would recognize any of these:
'2017-02-12 09:30:45'
'17-02-12 09:30:45'
170212093045
If we have a requirement to supply/specify literal values that represent integer milliseconds since '1970-01-01 00:00:00', we can use a SQL expression to convert those to values that can be compared to TIMESTAMP. As a demonstration:
SELECT '1970-01-01' + INTERVAL 1486857600000 / 1000 SECOND AS ts
If we need to supply integer millisecond values as a literal in a condition in a WHERE clause, then we can use expressions like the one above.
The query in the question could do something like this to compare the value in a TIMESTAMP column
AND time_stamp >= '1970-01-01' + INTERVAL 1486857600000 / 1000 SECOND
AND time_stamp < '1970-01-01' + INTERVAL 1486944000000 / 1000 SECOND