I have two tables one called slotLength and one called schedule. Here are their descriptions:
+------------+------+------+-----+----------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+------+------+-----+----------+-------+
| slotLength | time | NO | PRI | 00:00:00 | |
+------------+------+------+-----+----------+-------+
+-----------+-------------+------+-----+----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------+------+-----+----------+----------------+
| dayId | int(1) | NO | PRI | NULL | auto_increment |
| dayName | varchar(15) | YES | | NULL | |
| startHour | time | YES | | 08:00:00 | |
+-----------+-------------+------+-----+----------+----------------+
I know that they do not have the best design, but I am still learning. Also, they are just an experiment so please ignore the mistakes in their desigin.
Before I proceed, let's assume that slotLenght table contains just one row and let's call it's value slotSize.
I want to compute startHour + slotSize * n, where startHour represents values from startHour column in schedule table and n is a number. To be more specific, let's see an example,
if slotSize is "01:00:00" and a value from startHour is "09:00:00", then startHour +
slorSize * 3 I expect to have the value "12:00:00".
How the query should look like? Thank you.
I'm not sure you can multiply against a time field in SQL. Adding and subtracting is fairly easy, but multiplication would get a bit more complicated. You can use ADDTIME() for part of the equation, but I'm unsure of the multiplication part. Some heavier mathematics might have to come into play for that.
Here is a list of MySQL time functions
http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html
EDIT:
Perhaps something along the lines of converting to seconds, multiplying, and then converting back would work. I'm not overly familiar with MySQL so hopefully someone will give you the query your looking for, but this should get you started to try on your own.
SELECT ADDTIME(startHour, SEC_TO_TIME(TIME_TO_SEC(slotSize) * 3)) AS Calculated
FROM Table, OtherTable
Not sure if ^ Table is needed so if it works without it forget if not throw it in there to select startHour.
I believe this is close to what your looking for. As I said being unfamiliar with MySQL errors most likely lie in wait especially with the ADDTIME() function as I believe it requires the date portion to work.
Related
My SQL knowledge is rather weak and I come from procedural programming, so bear with me. I have a database that contains data from a weather station - these are collected each minute and the (important part of the) table is
MariaDB [weather]> describe readings;
+------------------+------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------+------------+------+-----+-------------------+-------+
| time | timestamp | NO | PRI | CURRENT_TIMESTAMP | |
| inside_temp | float | YES | | NULL | |
| outside_temp | float | YES | | NULL | |
+------------------+------------+------+-----+-------------------+-------+
I want to find all days where the outside_temp was not lower and not larger than some values.
I can code it externally using MySQL for queries like
select min(outside_temp), max(outside_temp) from readings where date(time)='2022-01-27';
and iterating over all days in the database to check temperature values for each day separately, but I wonder if it is possible to do the selection just using MySQL command (I suppose it is, just beyond my imagination).
Something like select date(time), min(outside_temp), max(outside_temp) from readings group by date(time); would give you all timestamps that meet the requirements
I want to weekly update a field in a MySQL table "Persons", with the avg of two fields of the "Tasks" table, end_date and start_date:
PERSON:
+----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+-------+
| average_speed | int(11) | NO | | 0 | |
+----------------+-------------+------+-----+---------+-------+
TASKS:
+----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+-------+
| person_id | int(11) | NO | | NULL | |
| start_date | date | NO | | NULL | |
| end_date | date | NO | | NULL | |
+----------------+-------------+------+-----+---------+-------+
(tables are not complete).
average_speed = AVG(task.end_date - task.start_date)
Now, the Tasks table is really big, and ** I don't want to compute the average on every task for every person every week**. (That's a solution, but I'm trying to avoid it).
What's the best way to update the average_speed?
I thought about adding two columns in the person's table:
"last_count": count of computed tasks since now for each person
"last_sum": last sum of (end_date - start_date) for each person
So that on a new update i could do something like average_speed = (last_sum+new_sum) / (last_count + new_count) where new_count is the sum of the tasks in the last week.
Is there a better solution/architecture?
EDIT:
to answer a comment, the query I would do is something like this:
SELECT
count(t.id) as last_count,
sum(TIMESTAMPDIFF(MINUTE, t.start_date, t.end_date)) as last_sum
avg(TIMESTAMPDIFF(MINUTE, t.start_date, t.end_date))
from tasks as t
where t.end_date BETWEEN DATE_SUB(CURDATE(), INTERVAL 1 WEEK) AND CURDATE()
And i can rely on a php script to get result and do some calculations
Having a periodic update to the table is a bad way to go for all the reasons you've listed above, and others.
If you have access to the code that writes to the Tasks table, that’s the best place to put the update. Add an Average field and calculate and set the value when you write the task end time.
If you don’t have access to the code, you can add a calculated field to the table that shows the average and let SQL figure it out during the execution of a query. This can slow queries down a little, but the data is always valid and SQL is smart enough to only calculate that value when it is needed.
A third (ugly) option is a trigger on the table that updates the value when appropriate. I’m not a fan of triggers because they hide business logic in unexpected places, but sometimes you just have to get the job done.
I've looked for solutions but couldn't find anything for my specific problem and can't manage to sort it on my own, the queries I'm trying are too heavy and timeout my server.
I have a table 'events' like this :
+-----------+--------------------------------+
| field | informations |
+-----------+--------------------------------+
| id | INT(11) PRIMARY AUTO_INCREMENT |
| repeat_id | INT(11) |
| timestamp | TIMESTAMP |
| title | VARCHAR(255) |
| details | TEXT |
+-----------+--------------------------------+
My events cane be unique ('repeat_id'=0) or repeated ('repeat_id'>0), and my problem is, I want to find all "outdated" events, that is to say the events that are repeated AND whose max timestamp is under current timestamp.
It might be easy using the good synthax and/or functions but I can't manage to do it... any help would be appreciated!
Thanks a lot,
Arthur
What if you try like below
select * from events
where repeat_id > 0
group by title
having max(`timestamp`) <= CURRENT_TIMESTAMP;
I am a total SQL noob; sorry.
I have a table
mysql> describe activity;
+--------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------+------+-----+---------+-------+
| user | text | NO | | NULL | |
| time_stamp | int(11) | NO | | NULL | |
| activity | text | NO | | NULL | |
| item | int | NO | | NULL | |
+--------------+---------+------+-----+---------+-------+
Normally activity is a two-step process; 1) "check out" and 2 "use"
An item cnnot be checked out a second time, unless used.
Now I want to find any cases where an item was checked out but not used.
Being dumb, I would use two selects, one for check out &one for use, on the same item, then compare the timestamps.
Is there a SELECT statemnt that will help me selct the items which were checked out but not used?
Tricky with the possibility of multipel checkouts. Or should I just code
loop over activity, form oldest until newset
if find a checkout and there is no newer used time then i have a hit
You could get the last date of each checkout or use and then compare them per item:
SELECT MAX(IF(activity='check out', time_stamp, NULL)) AS last_co,
MAX(IF(activity='use', time_stamp, NULL)) AS last_use
FROM activity
GROUP BY item
HAVING NOT(last_use >= last_co);
The NOT(last_use >= last_co) is written that way because of how NULL compare behaviour works: last_use < last_co will not work if last_use is null.
Without proper indexing, this query will not perform very well though. Plus you might want to bound the query using a WHERE condition.
I have a MySQL table with many numeric columns (some INT, some FLOAT). I would like to query it with the MySQL command-line client (specifically, mysql Ver 14.14 Distrib 5.1.41, for debian-linux-gnu (x86_64) using readline 6.1), like so:
SELECT * FROM table WHERE foo;
Unfortunately, if the value of any numeric field exceeds 10^6, this client displays the result in scientific notation, which makes reading the results difficult.
I could correct the problem by FORMAT-ing each of the fields in my query, but there are many of them and many tables I would like to query. Instead I'm hoping to find a client variable or flag I can set to disable scientific notation for all queries.
I have not been able to find one in the --help or the man page, nor searching Google or this site. Instead all I find are discussions of preserving/removing scientific notation when using <insert-programming-language>'s MySQL API.
Thank you for any tips.
::edit::
Here's an example table ...
mysql> desc foo;
+--------------+-------------+------+-----+-------------------+
| Field | Type | Null | Key | Default |
+--------------+-------------+------+-----+-------------------+
| date | date | NO | PRI | NULL |
| name | varchar(20) | NO | PRI | NULL |
| val | float | NO | | NULL |
| last_updated | timestamp | NO | | CURRENT_TIMESTAMP |
+--------------+-------------+------+-----+-------------------+
and some example values ...
mysql> select * from foo where date='20120207';
+------------+--------+--------------+---------------------+
| date | name | val | last_updated |
+------------+--------+--------------+---------------------+
| 2012-02-07 | A | 88779.5 | 2012-02-07 13:38:14 |
| 2012-02-07 | B | 1.00254e+06 | 2012-02-07 13:38:14 |
| 2012-02-07 | C | 78706.5 | 2012-02-07 13:38:15 |
+------------+--------+--------------+---------------------+
Now, the actual values I loaded into the third field are:
88779.5, 1002539.25, 78706.5390625
and they can be seen exactly if I manipulate the value:
mysql> select date, name, ROUND(val, 10), last_updated from foo where ...
+------------+---+--------------------+---------------------+
| 2012-02-07 | A | 88779.5000000000 | 2012-02-07 13:38:14 |
| 2012-02-07 | B | 1002539.2500000000 | 2012-02-07 13:38:14 |
| 2012-02-07 | C | 78706.5390625000 | 2012-02-07 13:38:15 |
Something in the client seems to be enforcing that I only be allowed to see six significant figures, even though there are more in the table.
If a query such as
mysql> select ROUND(*, 2) from foo ...
were possible, that would be great! Otherwise I can't really take the time to individually wrap 100 column names in "ROUND()" whenever I need to inspect some data.
Interestingly, I occasionally use a phpMyAdmin interface to browse the contents of some of these tables, and that interface also has this 6 significant figure limitation. So it's not limited to just the CLI.
Well, after reading the documentation more thoroughly, I still can't see any reason why a client would limit itself to displaying only 6 sig figs from a FLOAT (especially when the table itself is definitely storing more).
Nonetheless, an acceptable solution (for this weary user) is to change all my tables to use DECIMAL(16,4) instead of FLOAT. Unfortunately, this makes all my numbers show up with 4 decimal places (even if they're all '0'). But at least all numbers have the same width now, and my client never displays them in scientific notation or limits the number of sig figs in its output.
Wouldn't the CAST function allow you to request that the values for a certain field are returned as DECIMAL ? Not an expert and haven't tried it, but that would be the first thing I try.
I know this is old but this helped me.. I used a view..
create view foo2 as select date, name, ROUND(val, 10) val, last_updated from foo
Then just do your queries on foo2. also works in phpmyadmin