I created a table with a column containing numbers listed from 1 to 100. I want to delete numbers that divide by 3 without any remainder. Who can recommend me a way (script) to do that. Only logic I could make in this problem is that if the sum of digits of a number can divide by 3 that means any number which correspond to that case could be divisible.
If you are looking to delete the rows with number divisible completely by 3, you can use built-in modulus function
You could say something like this
delete
from myTable
where colNumber%3 = 0
This query should solve your problem
DELETE FROM table WHERE (id % 3) = 0;
Related
I have a table in PostgreSQL DB like this.
ID, Name, scores.
10, abc,{23,19,34}
11, def, {2333,233,24}
12, ghi, {321,34}
13,hio,{}
scores in the above data model is an array or list of numbers.
Now we have to find all students who has any single score which is 19 when divided by 10. How can I achieve this?
I tried this, but it doesn't work.
SELECT * FROM students where 19 = ANY(scores)/10
Some thing like this works. But we need a better solution(using an inverted index probably) as the rows are in the order of millions.
SELECT * FROM students where 190 <= ANY(scores) < 200
In your data example there is no record that meet your condition of some value that when divided by 10 is =19. But i understand that you are sure about your condition that single number from array when divided by 10 should be equal to 19. Not sum of all or something?
First do you have gin index on score column?
Second - really single numbers in your score array will be bigger then int limit? If not bigint will just slow your queries.
Consider bigint issue and if you have to have it then, else remove ::bigint from query below
SELECT * FROM students where
scores&&array[190,191,192,193,194,195,196,197,198,199]::bigint
It is ugly but probably faster then any tries of extract all number from array first then dividing them by 10 and then comparing to 19.
If you only search score for numbers that are equal 19 after dividing by 10, just use the method of Abelisto but it will be a killer during inserting as saving function index for milions of rows and long arrays will be slow.
I have a column in the sql server called "Ordinal" that is used to indicate the display order of the rows. It starts from 0 and skips 10 for the next row. so we have something like this:
Id Ordinal
1 0
2 20
3 10
It skips 10 because we wanted to be able to move item in between items (based on ordinal) without having to reassign ordinal number for the entire table.
As you can imagine eventually, Ordinal number will need to be reassign somehow for a move in between operation either on surrounding rows or for the entire table as the unused ordinal numbers between the target items are all used up.
Is there any algorithm that I can use to effectively reorder the ordinal number for the move operation taken in the consideration like long term maintainability of the table and minimizing update operations of the table?
You can re-number the sequences using a somewhat complicated UPDATE statement:
UPDATE u
SET u.sequence = 10 * (c.num_below-1)
FROM test u
JOIN (
SELECT t.id, count(*) AS num_below
FROM test t
JOIN test tr ON tr.sequence <= t.sequence
GROUP BY t.id
) c ON c.id=u.id
The idea is to obtain a count of items with the sequence lower than that of the current row, multiply the count by ten, and assign it as the new count.
The content of test before the UPDATE:
ID Sequence
__ ________
1 0
2 10
3 20
4 12
The content of test after the UPDATE:
ID Sequence
__ ________
1 0
2 30
3 10
4 20
Now the sequence numbers are evenly spread again, so you can continue inserting in the middle until you run out of new sequence numbers; then you can re-number again.
Demo.
These won't answer your question directly--I just thought I might suggest some other approaches:
One possibility--don't try to do it by hand. Have your software manage the numbers. If they need re-writing, just save them with new numbers.
a second--use a "Linked List" instead. In each record store the index of the next record you want displayed, then have your code load that directly into a linked list.
Yet another simple approach. Let's say you're inserting a new record with an ordinal equal x.
First, check if there's a row having ordinal value equal x. In case there's one, just update all the records having the ordinal value equal or bigger than x increasing them by y. Then, you are safe to insert a new record.
This way you're sure you'll not run update every time and of course, you'll keep the order.
Here is my code
select len(cast(code as float)),code
from tbl1
where code is not null
and this is the output:
I want a count of digits in the code column.
I don't understand why the last one is counted as 12 and not 8?
Cast it as an int instead:
select len(cast(code as int)), code
from tbl1
where code is not null;
Presumably, some sort of decimal values are getting counted.
Get the number's power of 10 and add 1. This works either if ints or reals to count the number of digits of the whole number part (note using LOG10 only works on positive numbers so I have applied ABS to get around this issue, may not be required for your data):
SELECT code, CASE WHEN Number = 0 THEN 1
ELSE FLOOR(LOG10(ABS(code))) + 1 AS NDigits
FROM tbl1
I found a good method of getting the next 4 digit number.
How to find next free unique 4-digit number
But in my case I want to get next available 4 or 5 digit number.
And this will change depending upon the users request. Theses number are not a key ID columns, but they are essential to the tagging structure for the business purpose.
Currently I use a table adabpter query. But how would I write a query.
I suppose I could do a long iterative loop through all values until I see a 4 digit.
But I'm trying to think of something more efficient.
Function GetNextAvailableNumber(NumofDigits) as Long
'SQL Code Here ----
'Query Number Table
Return Long
End Function
Here's my current SQL:
'This Queries my View
SELECT MIN([Number]) AS Expr1
FROM LineNumbersNotUsed
'This is my View SQL
SELECT Numbers.Number
FROM Numbers
WHERE (((Exists (Select * From LineList Where LineList.LineNum = Numbers.Number))=False))
ORDER BY Numbers.Number;
Numbers is the List of All available number from 0 to 99999, basically what's available to use.
LineList is my final master table where I keep the long and all the relevant other business information.
Hopefully this make sense.
Gosh you guys are so tough on new guys.
I accidentally hit the enter key, and the question posted and I instantly get -3 votes.
Give a new guy a break will you! Please.
I apologize in advance in case I overlooked something in your question. Using your design, won't a query like this return the next unused 4 digit number?
SELECT MIN([Number]) AS next_number
FROM LineNumbersNotUsed
WHERE
[Number] > 999
AND [Number] < 10000;
This approach is not adequate with multiple concurrent users, but you didn't indicate that is an issue for you.
The question you linked to explains that what you need is a table with 2 fields:
Number InUse
0000 No
0001 No
0002 Yes
0003 No
0005 Yes
Whenever a number is used/released, the table must be updated to set InUse to Yes/No.
Maybe I'm missing something, but from your explanation, and the SQL code you show us, it seems that you only have a table with a single field containing all numbers from 0 to 100000.
If that's the case, I don't see the usefulness of that table at all.
If I were you, and if I understand your need correctly, what you want is something like this:
First of all, create the table as above, with all running numbers from 0 to 100000, and a field for confirming if that number is used or not.
Initialise the InUse field with all the numbers already taken in your LineList table, something like:
UPDATE Numbers SET InUse = True
WHERE Numbers.Number IN (SELECT LineNum FROM LineList)
Write a function ReserveNumber(NumOfDigits as Integer) As Long to find and reserve a 4-digit or 5-digit free number following this logical sequence:
Depending on NumOfDigits (4 or 5) get the result of one of the queries as LowestNumber:
SELECT Min(Number) FROM Numbers WHERE Number < 10000 AND NOT InUse
SELECT Min(Number) FROM Numbers WHERE Number >= 10000 AND NOT InUse
Reserve that particular number to ensure it's not going to be used again:
UPDATE Numbers SET InUse = True WHERE Number = #LowestNumber
Return LowestNumber
Whenever
Notes: the logic above is a bit naive as it suppose that no two users will attempt to get the lowest number at the same time. There is however a risk that this may happen one day.
To remove that risk, you can, for instance, add a TakenBy column to the Numbers table and set it to the current username. Then, after you have reserved the number, read-it again to ensure that the TakenBy is really updated by the current client. If not, just try gain.
There are lots of ways to do this. You can try to fiddle around table locks as well, but whatever your solution, make sure you test it.
I have a process that needs to select rows from a Table (queued items) each row has a quantity column and I need to select rows where the quantities add to a specific multiple. The mulitple is the order of between around 4, 8, 10 (but could in theory be any multiple. (odd or even)
Any suggestions on how to select rows where the sum of a field is of a specified multiple?
My first thought would be to use some kind of MOD function which I believe in SQL server is the % sign. So the criteria would be something like this
WHERE MyField % 4 = 0 OR MyField % 8 = 0
It might not be that fast so another way might be to make a temp table containing say 100 values of the X times table (where X is the multiple you are looking for) and join on that