Let say I have a post table. But I want to query all today post. But if today post is less than 10 post, I will get back the yesterday post to query. If it is more than 10 posts, no need to query yesterday post....If SQL statement can't do it. Is this only achieve it by calling the post manually....? Thank you.
***The database is MySQL
Let me clarify the question in a typical example:
If today have 5 posts....ONLY. And yesterday have 10 posts.
return : 5 today posts, and 5 posts from yesterday
If today have 12 posts....ONLY.
And yesterday have 10 posts.
return : 12 today posts.
If today have 10 posts....ONLY. And yesterday have 10 posts.
return : 10 today posts.
If today have 2 posts....ONLY. yesterday have 5 posts, and the day before yesterday 5posts.
return : 2 today posts, 5 yesterday posts, 3 the day before yesterday posts.
You can try
select count(*) from post_table
where date = todays_date
and if the result is > 10 then
select * from post_table
where date = today's date
else
select * from post_table
order by date desc
limit 10
Just another idea, a little bit shorter:
set #i = 0;
select *, #i := #i + 1
from post_table
where #i < 10 or date = today
order by date desc;
Not sure it is very effective.
Update: it is fast!
I tested on the such sample:
create table a(i int primary key, d date not null, index idx(d))
set #i = 0;
insert into a(i, d)
select #i := #i + 1, adddate(curdate(), interval -(#i % 1000) day)
from <100 records> a, <100 records> b, <100 records> c
A tiny development on Jan S's solution (combines the two conditional SELECTs into one with a parametrised LIMIT):
SELECT #count := COUNT(*)
FROM post_table
WHERE date = today;
IF #count < 10 SET #count = 10;
SELECT *
FROM post_table
ORDER BY date DESC
LIMIT #count;
UPDATE
As stated in the documentation:
The LIMIT clause can be used to constrain the number of rows returned by the SELECT statement. LIMIT takes one or two numeric arguments, which must both be nonnegative integer constants, with these exceptions:
Within prepared statements, LIMIT parameters can be specified using ? placeholder markers.
Within stored programs, LIMIT parameters can be specified using integer-valued routine parameters or local variables.
That means, you can only use code like above in a stored procedure, not in a plain query you are issuing in your client application.
Related
I have 2 mysql tables spot_times - 10k rows and visit_times - 5.3 million rows.
I m trying to write a query that can join spot_times.spot_date on visit_times.visit_date based on a 10 minute window.
Both date fields are indexed and column type datetime.
I have written the following sql which takes hours to run.
Select spot_date, count(visit_date) total_visits
From spot_times st
Left
Join visit_times v
on v.visit_date between st.spot_date and st.spot_date + interval 10 minute
group by 1;
This query takes hours to run.
My explain plan looks like the query is not using the indexes.
Explain plan
Please help.
Range queries are notoriously difficult to get useful index performance with on large datasets.
You might be able to get some benefit out of partitioning visit_times by date range: https://dev.mysql.com/doc/refman/8.0/en/partitioning-range.html
Just thought it might be useful for anyone that came across the same issue.
I started off by adding an auto_increment column visit_id on the visits_times table ordered by visit_date field.
Idea is to get the visit_id nearest to st.spot_date and st.spot_date + interval 10 minute.Then subtracting the visit_id which should be the total visits between the range.
Created a function to return visit_id for a date and interval.Function uses the visit_date index and loops until it finds a record adding a second on every loop.
DELIMITER //
DROP function IF EXISTS `spot_time_function` //
CREATE function `spot_time_function`( p_datetime datetime, p_time int)
returns int
BEGIN
declare v_id int ;
declare z int;
set z = 0;
time_loop: LOOP
select visit_id into v_id from visit_times where visit_date = p_datetime + interval p_time minute + interval z second limit 1;
IF v_id is not null THEN
LEAVE time_loop;
END IF;
SET z = z + 1;
END LOOP;
return v_id;
END //
DELIMITER ;
So final query looks like.
Select
spot_date,
spot_time_function(spot_date,10) - spot_time_function(spot_date,0) as total_visit
From spot_times;
Above query runs in 0.110 sec.
I've written a stored procedure to iterate over every week for three years. It doesn't work though and returns a vague error message.
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 18
DELIMITER $$
CREATE PROCEDURE loop_three_years()
BEGIN
declare y INT default 2016;
declare m int default 4;
declare d int default 20;
WHILE y <= 2019 DO
WHILE YEARWEEK(concat(y, '-', m, '-', d)) <= 53 DO
WHILE m < 12 DO
WHILE (m = 2 and d <= 29) OR (d <=30 and m in(4, 6,9,11)) OR ( m in(1,3,5,7,8,10,12) AND d <= 31) DO
set d = d + 7;
SELECT YEARWEEK(concat(y, '-', m, '-', d));
END WHILE;
set d=1;
END WHILE;
set m = 1;
SET y = y + 1;
END WHILE;
END
$$
When I used this as minimal parts they work so I'm not sure what the issue is with my reassembly. Also not sure if there's a better way to do this. (The select is just for testing, it will be an insert when I use the real code.
Slightly Altered from a previous solution
You can build your own dynamic calendar / list using ANY other table in your system that has at least as many records as you need to fake row numbers. The query below will use MySQL # variables which work like an inline program and declaration. I can start the list with a given date... such as your 2016-04-20 and then each iteration through, add 1 week using date-based functions. No need for me to know or care about how many days have a 28, 29(leap-year), 30 or 31 days.
The table reference below of "AnyTableThatHasAtLeast156Records" is just that.. Any table in your database that has at least 156 records (52 weeks per year, 3 years)
select
YEARWEEK( #startDate ) WeekNum,
#startDate as StartOfWeek,
#startDate := date_add( #startDate, interval 1 week ) EndOfWeek
from
( select #startDate := '2016-04-20') sqlv,
AnyTableThatHasAtLeast156Records
limit
156
This will give you a list of 156 records (provided your "anyTable…" has 156 records all at once. If you need to join this to some other transaction table, you could do so by making the above a JOIN table. Benefit here, Since I included the begin date and end of week, those can be part of your joining to table.
Example, on
record WeekNum StartOfWeek EndOfWeek
1 ?? 2016-04-20 2016-04-27
2 ?? 2016-04-27 2016-05-04
3 ?? 2016-05-04 2016-05-11
4 ?? 2016-04-11 2016-05-18... etc
By adding 1 week to the starting point, you can see that it would do Ex: Monday to Monday. And the JOIN Condition below I have LESS THAN the EndOfWeek. This would account for any transactions UP TO but not including the ending date... such as transactions on 2016-04-26 11:59:59PM (hence LESS than 2016-04-27, as 04/27 is the beginning of the next week's cycle of transactions)
select
Cal.WeekNum,
YT.YourColumns
from
YourTransactionTable YT
JOIN ( aboveCalendarQuery ) Cal
on YT.TransactionDate >= Cal.StartOfWeek
AND YT.TransactionDate < Cal.EndOfWeek
where
whatever else
You could even do sum() with group by such as by WeekNum if that is what you intend.
Hopefully this is a much more accurate and efficient way to build out your calendar to run with and linking to transactions if you so needed to.
Response from comment.
You could by doing a join to a ( select 1 union select 2 union … select 156 ), but your choice. The ONLY reason for the "AnyTable…" is I am sure with any reasonable database with transactions you would have 156 records or more easily. It's sole purpose is to just allow a row for cycling through the iterations to dynamically create the rows.
Also much more sound than the looping mechanism you have run into to begin with. Nothing wrong with that, especially learning purposes, but if more efficient ways, doesn't that make more sense?
Per feedback from comment
I dont exactly know your other table you are trying to insert into, but yes, you can use this for all 3000 things. Provide more of what you are trying to do and I can adjust... In the mean-time, something like this...
insert into YourOtherTable
( someField,
AnotherField,
WeekNum
)
select
x.someField,
x.AnotherField,
z.WeekNum
from
Your3000ThingTable x
JOIN (select
YEARWEEK( #startDate ) WeekNum,
#startDate as StartOfWeek,
#startDate := date_add( #startDate, interval 1 week ) EndOfWeek
from
( select #startDate := '2016-04-20') sqlv,
AnyTableThatHasAtLeast156Records
limit
156 ) z
on 1=1
where
x.SomeCodition...
By joining the the select of 156 records on 1=1 (which is always true), it will return 156 entries for whatever record is in the Your3000ThingTable. So, if you have an inventory item table with
Item Name
1 Thing1
2 Thing2
3 Thing3
Your final insert would be
Item Name WeekNum
1 Thing1 1
1 Thing1 2
1 Thing1 ...
1 Thing1 156
2 Thing2 1
2 Thing2 2
2 Thing2 ...
2 Thing2 156
3 Thing3 1
3 Thing3 2
3 Thing3 ...
3 Thing3 156
And to pre-confirm what you THINK would happen, just try the select/join on 1=1 and you'll see all the records the query WOULD be inserting into your destination table.
I am currently working on a MySQL db with MySQL Workbench.
My objective is to retrieve the signups from a database to establish my company's KPIs on an Excel spreadsheet.
I wrote some sql queries that worked but I want to set up a very complete one in order to avoid using xxx different queries.
To get the signups for each month (based on 'created_at'), this makes the job:
SELECT year(u.created_at) year, monthname(u.created_at) month, COUNT(DISTINCT u.id) as 'New shoppers signups'
FROM users u
GROUP BY year, month
ORDER BY u.created_at
But I also wanted to have the total of previous signups for each month
Jan : 12
Feb : 14 (12 + 2 new signups)
March : 22 (14 + 8 new signups)
...
Where I get the sum of all the previous signups
I was thinking about something like:
DECLARE #month = '2012-01-01' //startdate
WHILE #month < curdate()
BEGIN
SELECT count(distinct u.id)
WHERE u.created_at < #month
dateadd(month, 1, #month) // incrementing to next month
END
But neither the while loop, the declare, set, or date function do work on MySQL Workbench.
I heard I have to declare procedures but I didn't have any more success...
I know I could use excel to get the result, but I want to improve my use of SQL and make this a very clear work.
You are actually close to the answer. Take your results and make that an inner query. Then that is basis of an outer query using MySQL variables to accumulate for each row.
select
pq.yearAdded,
pq.monthAdded,
pq.NewShoppers as 'New shoppers signups',
#runBal := #runBal + pq.NewShoppers as TotalNewShoppers
from
( SELECT
year(u.created_at) yearAdded,
monthname(u.created_at) monthAdded,
COUNT(DISTINCT u.id) as NewShoppers
from
users u
GROUP BY
year(u.created_at),
monthname(u.created_at)
ORDER BY
year(u.created_at),
monthname(u.created_at) ) pq,
( select #runBal := 0 ) sqlvars
I would just suggest having column names stay away from possible reserved words, such as Year, Month and other standard SQL commands and function names... otherwise you typically need to add tick-marks around the column names
I have some problems when coding SQL group by week.
I have a MySQL table named order.
In this entity, there are several attributes, called 'order_id', 'order_date', 'amount', etc.
I want to make a table to show the statistics of past 7 days order sales amount.
I think first I should get the today value.
Since I use Java Server Page, the code like this:
Calendar cal = Calendar.getInstance();
int day = cal.get(Calendar.DATE);
int Month = cal.get(Calendar.MONTH) + 1;
int year = cal.get(Calendar.YEAR);
String today = year + "-" + Month + "-" + day;
then, I need to use group by statement to calculate the SUM of past 7 day total sales amount.
like this:
ResultSet rs=statement.executeQuery("select order_date, SUM(amount) " +
"from `testing`.`order` GROUP BY order_date");
I have problem here. In my SQL, all order_date will be displayed.
How can I modify this SQL so that only display past seven days order sale amount?
Besides that, I discover a problem in my original SQL.
That is, if there is no sales on that day, no results would be displayed.
OF course, I know the ResultSet does not allow return null values in my SQL.
I just want to know if I need the past 7 order sales even the amount is 0 dollars,
Can I have other methods to show the 0?
Please kindly give me advices if you have idea.
Thank you.
Usually it occurs to create with a script or with a stored procedure a calendar table with all dates.
However if you prefer you can create a table with few dates (in your case dates of last week) with a single query.
This is an example:
create table orders(
id int not null auto_increment primary key,
dorder date,
amount int
) engine = myisam;
insert into orders (dorder,amount)
values (curdate(),100),
(curdate(),200),
('2011-02-24',50),
('2011-02-24',150),
('2011-02-22',10),
('2011-02-22',20),
('2011-02-22',30),
('2011-02-22',5),
('2011-02-19',10);
select t.cdate,sum(coalesce(o.amount,0)) as total
from (
select curdate() -
interval tmp.digit * 1 day as `cdate`
from (
select 0 as digit union all
select 1 union all
select 2 union all
select 3 union all
select 4 union all
select 5 union all
select 6 union all
select 7 ) as tmp) as t
left join orders as o
on t.cdate = o.dorder and o.dorder >= curdate() - interval 7 day
group by t.cdate
order by t.cdate desc
Hope that it helps. Regards.
To answer your question "How can I modify this SQL so that only display past seven days order sale amount?"
Modify the SQL statement by adding a where clause to it:
Where order_date >= #date_7days_ago
The value for this #date_7days_ago date variable can be set before your statement:
Select #date_7days_ago = dateadd(dd,-7,getdate())
Adding that where clause to your query will return only those records which order date is in the last seven days.
Hope this helps.
You can try using this:
ResultSet rs = statement.executeQuery(
"SELECT IFNULL(SUM(amount),0)
FROM table `testing`.`order`
WHERE order_date >= DATE_SUB('" + today + "', INTERVAL 7 DAY)"
);
This will get you the number of orders made in the last 7 days, and 0 if there were none.
I want to get the number of Registrations back from a time period (say a week), which isn't that hard to do, but I was wondering if it is in anyway possible to in MySQL to return a zero for days that have no registrations.
An example:
DATA:
ID_Profile datCreate
1 2009-02-25 16:45:58
2 2009-02-25 16:45:58
3 2009-02-25 16:45:58
4 2009-02-26 10:23:39
5 2009-02-27 15:07:56
6 2009-03-05 11:57:30
SQL:
SELECT
DAY(datCreate) as RegistrationDate,
COUNT(ID_Profile) as NumberOfRegistrations
FROM tbl_profile
WHERE DATE(datCreate) > DATE_SUB(CURDATE(),INTERVAL 9 DAY)
GROUP BY RegistrationDate
ORDER BY datCreate ASC;
In this case the result would be:
RegistrationDate NumberOfRegistrations
25 3
26 1
27 1
5 1
Obviously I'm missing a couple of days in between. Currently I'm solving this in my php code, but I was wondering if MySQL has any way to automatically return 0 for the missing days/rows. This would be the desired result:
RegistrationDate NumberOfRegistrations
25 3
26 1
27 1
28 0
1 0
2 0
3 0
4 0
5 1
This way we can use MySQL to solve any problems concerning the number of days in a month instead of relying on php code to calculate for each month how many days there are, since MySQL has this functionality build in.
Thanks in advance
No, but one workaround would be to create a single-column table with a date primary key, preloaded with dates for each day. You'd have dates from your earliest starting point right through to some far off future.
Now, you can LEFT JOIN your statistical data against it - then you'll get nulls for those days with no data. If you really want a zero rather than null, use IFNULL(colname, 0)
Thanks to Paul Dixon I found the solution. Anyone interested in how I solved this read on:
First create a stored procedure I found somewhere to populate a table with all dates from this year.
CREATE Table calendar(dt date not null);
CREATE PROCEDURE sp_calendar(IN start_date DATE, IN end_date DATE, OUT result_text TEXT)
BEGIN
SET #begin = 'INSERT INTO calendar(dt) VALUES ';
SET #date = start_date;
SET #max = SUBDATE(end_date, INTERVAL 1 DAY);
SET #temp = '';
REPEAT
SET #temp = concat(#temp, '(''', #date, '''), ');
SET #date = ADDDATE(#date, INTERVAL 1 DAY);
UNTIL #date > #max
END REPEAT;
SET #temp = concat(#temp, '(''', #date, ''')');
SET result_text = concat(#begin, #temp);
END
call sp_calendar('2009-01-01', '2010-01-01', #z);
select #z;
Then change the query to add the left join:
SELECT
DAY(dt) as RegistrationDate,
COUNT(ID_Profile) as NumberOfRegistrations
FROM calendar
LEFT JOIN
tbl_profile ON calendar.dt = tbl_profile.datCreate
WHERE dt BETWEEN DATE_SUB(CURDATE(),INTERVAL 6 DAY) AND CURDATE()
GROUP BY RegistrationDate
ORDER BY dt ASC
And we're done.
Thanks all for the quick replies and solution.