Say I have a table with an incrementing id column and a random positive non zero number.
id
rand
1
12
2
5
3
99
4
87
Write a query to return the rows which add up to a given number.
A couple rules:
Rows must be "consumed" in order, even if a later row makes it a a perfect match. For example, querying for 104 would be a perfect match for rows 1, 2, and 4 but rows 1-3 would still be returned.
You can use a row partially if there is more available than is necessary to add up to whatever is leftover on the number E.g. rows 1, 2, and 3 would be returned if your max number is 50 because 12 + 5 + 33 equals 50 and 90 is a partial result.
If there are not enough rows to satisfy the amount, then return ALL the rows. E.g. in the above example a query for 1,000 would return rows 1-4. In other words, the sum of the rows should be less than or equal to the queried number.
It's possible for the answer to be "no this is not possible with SQL alone" and that's fine but I was just curious. This would be a trivial problem with a programming language but I was wondering what SQL provides out of the box to do something as a thought experiment and learning exercise.
You didn't mention which RDBMS, but assuming SQL Server:
DROP TABLE #t;
CREATE TABLE #t (id int, rand int);
INSERT INTO #t (id,rand)
VALUES (1,12),(2,5),(3,99),(4,87);
DECLARE #target int = 104;
WITH dat
AS
(
SELECT id, rand, SUM(rand) OVER (ORDER BY id) as runsum
FROM #t
),
dat2
as
(
SELECT id, rand
, runsum
, COALESCE(LAG(runsum,1) OVER (ORDER BY id),0) as prev_runsum
from dat
)
SELECT id, rand
FROM dat2
WHERE #target >= runsum
OR #target BETWEEN prev_runsum AND runsum;
Related
I am looking for a simple clean method to obtain the sequence {1, 2, 3, 4, 5, 6, 7,...,1000000} in MS Access SQL. I thought of creating a table with a column that numbers from 1 to 100000 however, this is inefficient.
Is there a way of generating numbers 1 to 10000000 in MS Access using SQL?
I tried the GENERATE_SERIES() function but MS Access SQL does not support this function.
id | number
------------
1. | 1
2. | 2
3. | 3
4. | 4
5. | 5
6. | 6
7. | 7
8. | 8
Yes, and it is not painfull - use a Cartesian query.
First, create a small query returning 10 records:
SELECT
DISTINCT Abs([id] Mod 10) AS N
FROM
MSysObjects;
Save it as Ten.
Then run this simple query:
SELECT
[Ten_0].[N]+[Ten_1].[N]*10+[Ten_2].[N]*100+[Ten_3].[N]*1000+[Ten_4].[N]*10000+[Ten_5].[N]*100000 AS Id
FROM
Ten AS Ten_0,
Ten AS Ten_1,
Ten AS Ten_2,
Ten AS Ten_3,
Ten AS Ten_4,
Ten AS Ten_5
which, in two seconds, will return Id from 0 to 999999.
Very painful but you can do the following:
create table numbers (
id int autoincrement,
number int
);
-- 1 row
insert into numbers (number) values (1);
-- 2 rows
insert into numbers (number) select number from numbers;
-- 4 rows
insert into numbers (number) select number from numbers;
-- 8 rows
insert into numbers (number) select number from numbers;
-- repeat a total of 20 times
The value of number is always 1, but id increments. You can make them equal using an update:
update numbers
set number = id;
If this were SQL server you could use a recursive CTE to do this.
WITH number
AS
(
SELECT num = 1
UNION ALL
SELECT num + 1
from number
where num < 1000000
)
SELECT num FROM number
option(maxrecursion 0)
But you are asking about MS Access, since access does not support recursive CTEs, you can try doing it with a macro and insert it into a table and read it out?
I have a table with 50k records. Now I want to update one column of the table with a random number. The number should be 7 digits.
I don't want to do that with procedure or loop.
PinDetailId PinNo
--------------------
783 2722692
784 9888648
785 6215578
786 7917727
I have tried this code but not able to succeed. I need 7 digit number.
SELECT
FLOOR(ABS(CHECKSUM(NEWID())) / 2147483647.0 * 3 + 1) rn,
(FLOOR(2000 + RAND() * (3000 - 2000) )) AS rn2
FROM
[GeneratePinDetail]
Random
For a random number, you can use ABS(CHECKSUM(NewId())) % range + lowerbound:
(source: How do I generate random number for each row in a TSQL Select?)
INSERT INTO ResultsTable (PinDetailId, PinNo)
SELECT PinDetailId,
(ABS(CHECKSUM(NewId())) % 1000000 + 1000000) AS `PinNo`
FROM GeneratePinDetail
ORDER BY PinDetailId ASC;
Likely Not Unique
I cannot guarantee these will be unique; but it should be evenly distributed (equal chance of any 7 digit number). If you want to check for duplicates you can run this:
SELECT PinDetailId, PinNo
FROM ResultsTable result
INNER JOIN (
SELECT PinNo
FROM ResultsTable
GROUP BY PinNo
HAVING Count(1) > 1
) test
ON result.PinNo = test.PinNo;
You can create a sequence object and update your fields - it should automatically increment per update.
https://learn.microsoft.com/en-us/sql/t-sql/functions/next-value-for-transact-sql
Updated based on comment:
After retrieving the 'next value for' in the sequence, you can do operations on it to randomize. The sequence can basically be used then to create a unique seed for your randomization function.
If you don't want to create a function yourself, SQL Server has the RAND function build in already.
https://learn.microsoft.com/en-us/sql/t-sql/functions/rand-transact-sql
Consider the following table:
id gap groupID
0 0 1
2 3 1
3 7 2
4 1 2
5 5 2
6 7 3
7 3 3
8 8 4
9 2 4
Where groupID is the desired, computed column, such as its value is incremented whenever the gap column is greater than a threshold (in this case 6). The id column defines the sequential order of appearance of the rows (and it's already given).
Can you please help me figure out how to dynamically fill out the appropriate values for groupID?
I have looked in several other entries here in StackOverflow, and I've seen the usage of sum as an aggregate for a window function. I can't use sum because it's not supported in MonetDB window functions (only rank, dense_rank, and row_num). I can't use triggers (to modify the record insertion before it takes place) either because I need to keep the data mentioned above within a stored function in a local temporary table -- and trigger declarations are not supported in MonetDB function definitions.
I have also tried filling out the groupID column value by reading the previous table (id and gap) into another temporary table (id, gap, groupID), with the hope that this would force a row-by-row operation. But this has failed as well because it gives the groupID 0 to all records:
declare threshold int;
set threshold = 6;
insert into newTable( id, gap, groupID )
select A.id, A.gap,
case when A.gap > threshold then
(select case when max(groupID) is null then 0 else max(groupID)+1 end from newTable)
else
(select case when max(groupID) is null then 0 else max(groupID) end from newTable)
end
from A
order by A.id asc;
Any help, tip, or reference is greatly appreciated. It's been a long time already trying to figure this out.
BTW: Cursors are not supported in MonetDB either --
You can assign the group using a correlated subquery. Simply count the number of previous values that exceed 6:
select id, gap,
(select 1 + count(*)
from t as t2
where t2.id <= t.id and t2.gap > 6
) as Groupid
from t;
I have a table inside a PostgreSQL database with columns c1,c2...cn. I want to run a query that compares each row against a tuple of values v1,v2...vn. The query should not return an exact match but should return a list of rows ordered in descending similarity to the value vector v.
Example:
The table contains sports records:
1,USA,basketball,1956
2,Sweden,basketball,1998
3,Sweden,skating,1998
4,Switzerland,golf,2001
Now when I run a query against this table with v=(Sweden,basketball,1998), I want to get all records that have a similarity with this vector, sorted by number of matching columns in descending order:
2,Sweden,basketball,1998 --> 3 columns match
3,Sweden,skating,1998 --> 2 columns match
1,USA,basketball,1956 --> 1 column matches
Row 4 is not returned because it does not match at all.
Edit: All columns are equally important. Although, when I really think of it... it would be a nice add-on if I could give each column a different weight factor as well.
Is there any possible SQL query that would return the rows in a reasonable amount of time, even when I run it against a million rows?
What would such a query look like?
SELECT * FROM countries
WHERE country = 'sweden'
OR sport = 'basketball'
OR year = 1998
ORDER BY
cast(country = 'sweden' AS integer) +
cast(sport = 'basketball' as integer) +
cast(year = 1998 as integer) DESC
It's not beautiful, but well. You can cast the boolean expressions as integers and sum them.
You can easily change the weight, by adding a multiplicator.
cast(sport = 'basketball' as integer) * 5 +
This is how I would do it ... the multiplication factors used in the case stmts will handle the importance(weight) of the match and they will ensure that those records that have matches for columns designated with the highest weight will come up top even if the other columns don't match for those particular records.
/*
-- Initial Setup
-- drop table sport
create table sport (id int, Country varchar(20) , sport varchar(20) , yr int )
insert into sport values
(1,'USA','basketball','1956'),
(2,'Sweden','basketball','1998'),
(3,'Sweden','skating','1998'),
(4,'Switzerland','golf','2001')
select * from sport
*/
select * ,
CASE WHEN Country='sweden' then 1 else 0 end * 100 +
CASE WHEN sport='basketball' then 1 else 0 end * 10 +
CASE WHEN yr=1998 then 1 else 0 end * 1 as Match
from sport
WHERE
country = 'sweden'
OR sport = 'basketball'
OR yr = 1998
ORDER BY Match Desc
It might help if you wrote a stored procedure that calculates a "similarity metric" between two rows. Then your query could refer to the return value of that procedure directly rather than having umpteen conditions in the where-expression and the order-by-expression.
I have SQL table in which I have column and Probability . I want to select one row from it with randomly but I want to give more chances to the more waighted probability. I can do this by
Order By abs(checksum(newid()))
But the difference between Probabilities are too much so it gives more chance to highest probability.Like After picking 74 times that value it pick up another value for once than again around 74 times.I want to reduce this .Like I want 3-4 times to it and than others and all. I am thinking to give Range to the Probabilies.Its Like
Row[i] = Row[i-1]+Row[i]
How can I do this .Do I need to create function?Is there any there any other way to achieve this.I am neewby.Any help will be appriciated.Thank You
EDIT:
I have solution of my problem . I have one question .
if I have table as follows.
Column1 Column2
1 50
2 30
3 20
can i get?
Column1 Column2 Column3
1 50 50
2 30 80
3 20 100
Each time I want to add value with existing one.Is there any Way?
UPDATE:
Finally get the solution after 3 hours,I just take square root of my probailities that way I can narrow the difference bw them .It is like I add column with
sqrt(sqrt(sqrt(Probability)))....:-)
I'd handle it by something like
ORDER BY rand()*pow(<probability-field-name>,<n>)
for different values of n you will distort the linear probabilities into a simple polynomial. Small values of n (e.g. 0.5) will compress the probabilities to 1 and thus make less probable choices more probable, big values of n (e.g. 2) will do the opposite and further reduce probability of already inprobable values.
Since the difference in probabilities is too great, you need to add a computed field with a revised weighting that has a more even probability distribution. How you do that depends on your data and preferred distribution. One way to do it is to "normalize" the weighting to an integer between 1 and 10 so that the lowest probability is never more than ten times smaller than the highest.
Answer to your recent question:
SELECT t.Column1,
t.Column2,
(SELECT SUM(Column2)
FROM table t2
WHERE t2.Column1 <= t.Column1) Column3
FROM table t
Here is a basic example how to select one row from the table with taking into account the assigned row weights.
Suppose we have table:
CREATE TABLE TableWithWeights(
Id int NOT NULL PRIMARY KEY,
DataColumn nvarchar(50) NOT NULL,
Weight decimal(18, 6) NOT NULL -- Weight column
)
Let's fill table with sample data.
INSERT INTO TableWithWeights VALUES(1, 'Frequent', 50)
INSERT INTO TableWithWeights VALUES(2, 'Common', 30)
INSERT INTO TableWithWeights VALUES(3, 'Rare', 20)
This is the query that returns one random row with taking into account given row weights.
SELECT * FROM
(SELECT tww1.*, -- Select original table data
-- Add column with the sum of all weights of previous rows
(SELECT SUM(tww2.Weight)- tww1.Weight
FROM TableWithWeights tww2
WHERE tww2.id <= tww1.id) as SumOfWeightsOfPreviousRows
FROM TableWithWeights tww1) as tww,
-- Add column with random number within the range [0, SumOfWeights)
(SELECT RAND()* sum(weight) as rnd
FROM TableWithWeights) r
WHERE
(tww.SumOfWeightsOfPreviousRows <= r.rnd)
and ( r.rnd < tww.SumOfWeightsOfPreviousRows + tww.Weight)
To check query results we can run it for 100 times.
DECLARE #count as int;
SET #count = 0;
WHILE ( #count < 100)
BEGIN
-- This is the query that returns one random row with
-- taking into account given row weights
SELECT * FROM
(SELECT tww1.*, -- Select original table data
-- Add column with the sum of all weights of previous rows
(SELECT SUM(tww2.Weight)- tww1.Weight
FROM TableWithWeights tww2
WHERE tww2.id <= tww1.id) as SumOfWeightsOfPreviousRows
FROM TableWithWeights tww1) as tww,
-- Add column with random number within the range [0, SumOfWeights)
(SELECT RAND()* sum(weight) as rnd
FROM TableWithWeights) r
WHERE
(tww.SumOfWeightsOfPreviousRows <= r.rnd)
and ( r.rnd < tww.SumOfWeightsOfPreviousRows + tww.Weight)
-- Increase counter
SET #count += 1
END
PS The query was tested on SQL Server 2008 R2. And of course the query can be optimized (it's easy to do if you get the idea)