I am working with MySQL.
I have some queries that begin like this:
WITH dates (start_date, end_date) AS (
SELECT '2020-11-01', '2020-11-02'
UNION ALL SELECT '2020-11-02', '2020-11-03',
UNION ALL SELECT '2020-11-03', '2020-11-04')
SELECT dates.start_date, dates.end_date, id, COUNT(*)
FROM dates
INNER JOIN ...
I also sometimes need to run the same query, but with each date range being a week (Monday to Sunday), or a calendar month. Moreover, sometimes there are 100 or more of these, which is quite prone to typos in addition to occupying a lot of lines and taking a long time to write.
Is there more elegant and flexible way to achieve this ? Ideally I would like to be able to just specify a overall start date, an overall end date and a period (daily, weekly, monthly, yearly etc)
You can use a recursive CTE:
with recursive dates as (
select date('2020-11-01') as start_date, date('2020-11-02') as end_date
union all
select start_date + interval 1 day, end_date + interval 1 day
from dates
where start_date < '2020-12-01'
)
select *
from dates;
Here is a db<>fiddle. Of course, the logic would be a little different for months.
Create some date_ranges table which stores: series identifier, range number, range boundaries.
Insert needed series into it each time when you need a series which is not present in this table yet.
Use this table as source table in your query (maybe with additional condition which narrows the range if needed).
Remove series which will be used never in future.
Related
Since few days, I am trying to count records per hour from the MySQL database.
I have a table with a lot of records and I have column DATE and column TIME where in DATE I have the date of the record in the format 2022-05-19, and in the column TIME, I have the time of the record in the format 14:59:38.
What I am trying is to count every single day how many records per hour I have. Something like this:
DATE HOUR PCS
22-05-18 06-07 11
22-05-18 08-09 20
......... ..... ..
....... 21-22 33
I have tried many different ways but no success.
For example:
SELECT 'Date', count(*) FROM `root4`
where
DATE between '2022-05-01' and '2022-05-1' AND
TIME BETWEEN '06:11:05' AND '07:11:05'
Any help is highly evaluated.
I would recommend not using reserved words for columns, as you will have to escape them a lot. https://dev.mysql.com/doc/refman/8.0/en/keywords.html
If you stored TIME as a timestamp, you can extract the hour using the HOUR() function and group by that:
SELECT
`DATE`,
HOUR(`TIME`) AS `HOUR`,
COUNT(1)
FROM your_table
GROUP BY
`DATE`,
HOUR(`TIME`)
If you happened to store it as text you can use REGEXP_SUBSTR to get the hour value from your time string.
SELECT
`DATE`,
CAST(REGEXP_SUBSTR(`TIME`, '[0-9]+') AS UNSIGNED) AS `HOUR`,
COUNT(1)
FROM your_table
GROUP BY
`DATE`,
CAST(REGEXP_SUBSTR(`TIME`, '[0-9]+') AS UNSIGNED)
You can format your HOUR column how you want, like displaying 01-02 instead of 1 by using CONCAT, but this is your basic setup.
I have 2 tables, one with hostels (effectively a single-room hotel with lots of beds), and the other with bookings.
Hostel table: unique ID, total_spaces
Bookings table: start_date, end_date, num_guests, hostel_ID
I need a (My)SQL query to generate a list of all hostels that have at least num_guests free spaces between start_date and end_date.
Logical breakdown of what I'm trying to achieve:
For each hostel:
Get all bookings that overlap start_date and end_date
For each day between start_date and end_date, sum the total bookings for that day (taking into account num_guests for each booking) and compare with total_spaces, ensuring that there are at least num_guests spaces free on that day (if there aren't on any day then that hostel can be discounted from the results list)
Any suggestions on a query that would do this please? (I can modify the tables if necessary)
I built an example for you here, with more comments, which you can test out:
http://sqlfiddle.com/#!9/10219/9
What's probably tricky for you is to join ranges of overlapping dates. The way I would approach this problem is with a DATES table. It's kind of like a tally table, but for dates. If you join to the DATES table, you basically break down all the booking ranges into bookings for individual dates, and then you can filter and sum them all back up to the particular date range you care about. Helpful code for populating a DATES table can be found here: Get a list of dates between two dates and that's what I used in my example.
Other than that, the query basically follows the logical steps you've already outlined.
Ok, if you are using mysql 8.0.2 and above, then you can use window functions. In such case you can use the solution bellow. This solution does not need to compute the number of quests for each day in the query interval, but only focuses on days when there is some change in the number of hostel guests. Therefore, there is no helping table with dates.
with query as
(
select * from bookings where end_date > '2017-01-02' and start_date < '2017-01-05'
)
select hostel.*, bookingsSum.intervalMax
from hostel
join
(
select tmax.id, max(tmax.intervalCount) intervalMax
from
(
select hostel.id, t.dat, sum(coalesce(sum(t.gn),0)) over (partition by t.id order by t.dat) intervalCount
from hostel
left join
(
select id, start_date dat, guest_num as gn from query
union all
select id, end_date dat, -1 * guest_num as gn from query
) t on hostel.id = t.id
group by hostel.id, t.dat
) tmax
group by tmax.id
) bookingsSum on hostel.id = bookingsSum.id and hostel.total_spaces >= bookingsSum.intervalMax + <num_of_people_you_want_accomodate>
demo
It uses a simple trick, where each start_date represents +guest_num to the overall number of quests and each 'end_date' represents -guest_num to the overall number of quests. We than do the necessary sumarizations in order to find peak number of quests (intervalMax) in the query interval.
You change '2017-01-05' in my query to '2017-01-06' (then only two hostels are in the result) and if you use '2017-01-07' then just hostel id 3 is in the result, since it does not have any bookings yet.
I have attendance data for employees stored in the table attendance with the following column names:
emp_id (employee ID)
date
type (leave, absent, etc.)
(there are others but I'm omitting them for the sake of simplicity)
My objective is to retrieve all dates of the given month on which the employee was on leave (type = 'Leave') and the last leave taken in the last month, if any.
It's easy to do it using two queries (I'm using PHP to get process the data), but is there any way this can be done in a single query?
I'm answering my own question so as to close it. As #bpgergo pointed out in the comments, UNION will do the trick here.
SELECT * FROM table_name
WHERE type="Leave" AND
date <= (CURRENT_DATE() - 30)
Select the fields, etc you want then se a combined where clause using mysql's CURRENT_DATE() function. I subtracted 30 for 30 days in a month.
If date is a date column, this will return everyone who left 1 month or longer ago.
Edit:
If you want a specific date, change the 2nd month like this:
date <= (date_number - 30)
first of all sorry for that title, but I have no idea how to describe it:
I'm saving sessions in my table and I would like to get the count of sessions per hour to know how many sessions were active over the day. The sessions are specified by two timestamps: start and end.
Hopefully you can help me.
Here we go:
http://sqlfiddle.com/#!2/bfb62/2/0
While I'm still not sure how you'd like to compare the start and end dates, looks like using COUNT, YEAR, MONTH, DAY, and HOUR, you could come up with your desired results.
Possibly something similar to this:
SELECT COUNT(ID), YEAR(Start), HOUR(Start), DAY(Start), MONTH(Start)
FROM Sessions
GROUP BY YEAR(Start), HOUR(Start), DAY(Start), MONTH(Start)
And the SQL Fiddle.
What you want to do is rather hard in MySQL. You can, however, get an approximation without too much difficulty. The following counts up users who start and stop within one day:
select date(start), hour,
sum(case when hours.hour between hour(start) and hours.hour then 1 else 0
end) as GoodEstimate
from sessions s cross join
(select 0 as hour union all
select 1 union all
. . .
select 23
) hours
group by date(start), hour
When a user spans multiple days, the query is harder. Here is one approach, that assumes that there exists a user who starts during every hour:
select thehour, count(*)
from (select distinct date(start), hour(start),
(cast(date(start) as datetime) + interval hour(start) hour as thehour
from sessions
) dh left outer join
sessions s
on s.start <= thehour + interval 1 hour and
s.end >= thehour
group by thehour
Note: these are untested so might have syntax errors.
OK, this is another problem where the index table comes to the rescue.
An index table is something that everyone should have in their toolkit, preferably in the master database. It is a table with a single id int primary key indexed column containing sequential numbers from 0 to n where n is a number big enough to do what you need, 100,000 is good, 1,000,000 is better. You only need to create this table once but once you do you will find it has all kinds of applications.
For your problem you need to consider each hour and, if I understand your problem you need to count every session that started before the end of the hour and hasn't ended before that hour starts.
Here is the SQL fiddle for the solution.
What it does is use a known sequential number from the indextable (only 0 to 100 for this fiddle - just over 4 days - you can see why you need a big n) to link with your data at the top and bottom of the hour.
I'm not sure if this is even within the scope of MySQL to be honest or if some php is necessary here to parse the data. But if it is... some kind of stored procedure is likely necessary.
I have a table that stores rows with a timestamp and an amount.
My query is dynamic and will be searching based on a user-provided date range. I would like to retrieve the SUM() of the amounts for each day in a table that are between the date range. including a 0 if there are no entries for a given day
Something to the effect of...
SELECT
CASE
WHEN //there are entries present at a given date
THEN SUM(amount)
ELSE 0
END AS amountTotal,
//somehow select the day
FROM thisTableName T
WHERE T.timeStamp BETWEEN '$start' AND '$end'
GROUP BY //however I select the day
This is a two parter...
is there a way to select a section of a returned column? Like some kind of regex within mysql?
Is there a way to return the 0's for dates with no rows?
select * from thisTableName group by date(created_at);
In your case, it would be more like
SELECT id, count(id) as amountTotal
FROM thisTableName
WHERE timeStamp BETWEEN '$start' AND '$end'
GROUP BY DATE(timeStamp);
Your question is a duplicate so far: link.