Let's say I have a table like so, where the amount is some arbitrary amount of something(like fruit or something but we don't care about the type)
row | amount
_______________
1 | 54
2 | 2
3 | 102
4 | 102
5 | 1
And I want to select the rows that have the maximum value within a given interval. For instance if I was only wanting to select from rows 2-5 what would be returned would be
row | amount
_______________
3 | 102
4 | 102
Because they both contain the max value within the interval, which is 102. Or if I chose to only look at rows 1-2 it would return
row | amount
_______________
1 | 54
Because the maximum value in the interval 1-2 only exists in row 1
I tried to use a variety of:
amount= (select MAX(amount) FROM arbitraryTable)
But that will only ever return
row | amount
_______________
3 | 102
4 | 102
Because 102 is the absolute max of the table. Can you find the maximum value between a given interval?
I would use rank() or max() as a window function:
select t.row, t.amount
from (select t.*, max(amount) over () as maxamount
from t
where row between 2 and 4
) t
where amount = maxamount;
You can use a subquery to get the max value and use it in WHERE clause:
SELECT
row,
amount
FROM
arbitraryTable
WHERE
row BETWEEN 2 AND 5 AND
amount = (
SELECT
MAX(amount)
FROM
arbitraryTable
WHERE
row BETWEEN 2 AND 5
);
Just remember to use the same conditions in the main and sub query: row BETWEEN 2 AND 5.
Related
My database is Db2 for IBM i.
I have read-only access, so my query must use only basic SQL select commands.
==============================================================
Goal:
I want to select every record in the table until the sum of the amount column exceeds the predetermined limit.
Example:
I want to match every item down the table until the sum of matched values in the "price" column >= $9.00.
The desired result:
Is this possible?
You may use sum analytic function to calculate running total of price and then filter by its value:
with a as (
select
t.*,
sum(price) over(order by salesid asc) as price_rsum
from t
)
select *
from a
where price_rsum <= 9
SALESID | PRICE | PRICE_RSUM
------: | ----: | ---------:
1001 | 5 | 5
1002 | 3 | 8
1003 | 1 | 9
db<>fiddle here
I have a table of ids and quantities that looks like this:
dbo.Quantity
id | qty
-------
1 | 3
2 | 6
I would like to split the quantity column into multiple lines and number them, but with a set limit (which can be arbitrary) on the maximum quantity allowed for each row.
So for the value of 2, expected output should be:
dbo.DesiredResult
id | qty | bucket
---------------
1 | 2 | 1
1 | 1 | 2
2 | 1 | 2
2 | 2 | 3
2 | 2 | 4
2 | 1 | 5
In other words,
Running SELECT id, SUM(qty) as qty FROM dbo.DesiredResult should return the original table (dbo.Quantity).
Running
SELECT id, SUM(qty) as qty FROM dbo.DesiredResult GROUP BY bucket
should give you this table.
id | qty | bucket
------------------
1 | 2 | 1
1 | 2 | 2
2 | 2 | 3
2 | 2 | 4
2 | 1 | 5
I feel I can do this with cursors imperitavely, looping over each row, keeping a counter that increments and resets as the "max" for each is filled. But this is very "anti-SQL" I feel there is a better way around this.
One approach is recursive CTE which emulates cursor sequentially going through rows.
Another approach that comes to mind is to represent your data as intervals and intersections of intervals.
Represent this:
id | qty
-------
1 | 3
2 | 6
as intervals [0;3), [3;9) with ids being their labels
0123456789
|--|-----|
1 2 - id
It is easy to generate this set of intervals using running total SUM() OVER().
Represent your buckets also as intervals [0;2), [2;4), [4;6), etc. with their own labels
0123456789
|-|-|-|-|-|
1 2 3 4 5 - bucket
It is easy to generate this set of intervals using a table of numbers.
Intersect these two sets of intervals preserving information about their labels.
Working with sets should be possible in a set-based SQL query, rather than a sequential cursor or recursion.
It is bit too much for me to write down the actual query right now. But, it is quite possible that ideas similar to those discussed in Packing Intervals by Itzik Ben-Gan may be useful here.
Actually, once you have your quantities represented as intervals you can generate required number of rows/buckets on the fly from the table of numbers using CROSS APPLY.
Imagine we transformed your Quantity table into Intervals:
Start | End | ID
0 | 3 | 1
3 | 9 | 2
And we also have a table of numbers - a table Numbers with column Number with values from 0 to, say, 100K.
For each Start and End of the interval we can calculate the corresponding bucket number by dividing the value by the bucket size and rounding down or up.
Something along these lines:
SELECT
Intervals.ID
,A.qty
,A.Bucket
FROM
Intervals
CROSS APPLY
(
SELECT
Numbers.Number + 1 AS Bucket
,#BucketSize AS qty
-- it is equal to #BucketSize if the bucket is completely within the Start and End boundaries
-- it should be adjusted for the first and last buckets of the interval
FROM Numbers
WHERE
Numbers.Number >= Start / #BucketSize
AND Numbers.Number < End / #BucketSize + 1
) AS A
;
You'll need to check and adjust formulas for errors +-1.
And write some CASE WHEN logic for calculating the correct qty for the buckets that happen to be on the lower and upper boundary of the interval.
Use a recursive CTE:
with cte as (
select id, 1 as n, qty
from t
union all
select id, n + 1, qty
from cte
where n + 1 < qty
)
select id, n
from cte;
Here is a db<>fiddle.
Here is a table called packages:
id packages_sent date sent_order
1 | 10 | 2017-02-11 | 1
2 | 25 | 2017-03-15 | 1
3 | 5 | 2017-04-08 | 1
4 | 20 | 2017-05-21 | 1
5 | 25 | 2017-05-21 | 2
6 | 5 | 2017-06-19 | 1
This table shows the number of packages sent on a given date; if there were multiple packages sent on the same date (as is the case with rows 4 and 5), then the sent_order keeps track of the order in which they were sent.
I am trying to make a query that will return sum(packages_sent) given the following conditions: first, return the row with the max(date) (given some date provided), and second, if there are multiple rows with the same max(date), return the row with the max(send_order) (the highest send_order value).
Here is the query I have so far:
SELECT sum(packages_sent)
FROM packages
WHERE date IN
(SELECT max(date)
FROM packages
WHERE date <= '2017-05-29');
This query correctly finds the max date, which is 2017-05-21, but then for the sum it returns 45 because it is adding rows 4 and 5 together.
I want the query to return the max(date), and if there are multiple rows with the same max(date), then return the row with the max(sent_order). Using the example above with the date 2017-05-29, it should only return 25.
I don't see where a sum() comes into play. You seem to only want the last row:
select p.*
from packages p
order by date desc, sendorder desc
fetch first 1 row only;
If you data is truly ordered ascending as you show it then it's easier to use the surrogate key ID field.
SELECT packages_sent
FROM packages
WHERE ID =
(SELECT max(ID)
FROM packages
WHERE date <= '2017-05-29');
Since the ID is always increasing with date and sent order finding the max of it also finds the max of the other two in one step.
I have a table car that looks like this:
| mileage | carid |
------------------
| 30 | 1 |
| 50 | 1 |
| 100 | 1 |
| 0 | 2 |
| 70 | 2 |
I would like to get the average difference for each car. So for example for car 1 I would like to get ((50-30)+(100-50))/2 = 35. So I created the following query
SELECT AVG(diff),carid FROM (
SELECT (mileage-
(SELECT Max(mileage) FROM car Where mileage<mileage AND carid=carid GROUP BY carid))
AS diff,carid
FROM car GROUP BY carid)
But this doesn't work as I'm not able to use current row for the other column. And I'm quite clueless on how to actually solve this in a different way.
So how would I be able to obtain the value of the next row somehow?
The average difference is the maximum minus he minimum divided by one less than the count (you can do the arithmetic to convince yourself this is true).
Hence:
select carid,
( (max(mileage) - min(mileage)) / nullif(count(*) - 1, 0)) as avg_diff
from cars
group by carid;
I have a table of persons:
id | Name | Age
1 | Alex | 18
2 | Peter| 30
3 | Zack | 25
4 | Bim | 30
5 | Ken | 20
And I have the following interval of rows: WHERE ID>1 AND ID<5. I know that in this interval there is a person whose id=3. What is the most efficient (the fastest) way to get its row number in this interval (in my example rownumber=2)? I mean I don't need any other data. I need only one thing - to know row position of person with id=3 in interval WHERE ID>1 AND ID<5.
If it's possible I would like to get not vendor specific solution but a general sql solution. If it's not possible then I need solution for postgresql and h2.
The row number would be the number of rows between the first row in the interval and the row you're looking for. For interval ID>1 AND ID<5 and target row ID=3, this is:
select count(*)
from YourTable
where id between 2 and 3
For interval ID>314 AND ID<1592 and target row ID=1000, you'd use:
where id between 315 and 1000
To be sure that there is an element with ID=3, use:
select count(*)
from YourTable
where id between 2 and
(
select id
from YourTable
where id = 3
)
This will return 0 if the row doesn't exist.