I have a table like so:
id device group
-----------------
1 a 1000
2 a 1000
3 b 1001
4 b 1001
5 b 1001
6 b 1002
8 a 1003
9 a 1003
10 a 1003
11 a 1003
12 b 1004
13 b 1004
All id's and groups are sequential. What I would like is to select id and device based on groups and devices. Think of it as a pagination type selection. Getting the last group is a simple inner selection, but how do I select the second last group, or the third last group - etc.
I tried the row number function like this:
SELECT * FROM
( SELECT *, ROW_NUMBER() OVER (PARTITION BY device ORDER BY group DESC) rn FROM data) tmp
WHERE rn = 1;
.. but changing rn is giving me the previous id, not the previous group.
I would like to end up with a selection that could accomodate these results:
device = a, group = latest:
id device group
10 a 1003
11 a 1003
device = a, group = latest - 1:
id device group
1 a 1000
2 a 1000
Any one know how to accomplish this?
Edit:
Use case is a GPS enabled device in a car, sending data every 30 seconds. Imagine going on a drive today. First you go to the shops, then you go home. the first trip is you driving to the shop. The second trip is you driving back. I want to show those trips on a map, but it means I need to identify your last trip, and then the trip before it - ad infinitum, until you run out of trips.
You can try this approach:
`with x as (
select distinct page
from test_table),
y as (
select x.page
,row_number() over (order by page desc) as row_num
from x)
select test_table.* from test_table join y on y.page = test_table.page
where y.row_num =2`
I will try to explain what I have did here.
The first block(x) returns the distinct groups(pages in my case).
The second block(y) assigns row numbers to the groups in terms of their rank. In this case the ranking is in descending order of the pages.
Finally the third block, selects the desired value for the desired page. In case you want the pen-ultimate page , type rouw_num=2, if third from last use row_num =3 and likewise.
You can play around with the values [here]: http://sqlfiddle.com/#!15/190c06/26
Use dense_rank():
select d.*
from (select d.*, dense_rank() over (order by group_id desc) as seqnum
from data d
where device = 'a'
) d
where seqnum = 2;
Related
How to repeat rows based on column value in snowflake using sql.
I tried a few methods but not working such as dual and connect by.
I have two columns: Id and Quantity.
For each ID, there are different values of Quantity.
So if you have a count, you can use a generator:
with ten_rows as (
select row_number() over (order by null) as rn
from table(generator(ROWCOUNT=>10))
), data(id, count) as (
select * from values
(1,2),
(2,4)
)
SELECT
d.*
,r.rn
from data as d
join ten_rows as r
on d.count >= r.rn
order by 1,3;
ID
COUNT
RN
1
2
1
1
2
2
2
4
1
2
4
2
2
4
3
2
4
4
Ok let's start by generating some data. We will create 10 rows, with a QTY. The QTY will be randomly chosen as 1 or 2.
Next we want to duplicate the rows with a QTY of 2 and leave the QTY =1 as they are.
Obviously you can change all parameters above to suit your needs - this solution works super fast and in my opinion way better than table generation.
Simply stack SPLIT_TO_TABLE(), REPEAT() with a LATERAL() join and voila.
WITH TEN_ROWS AS (SELECT ROW_NUMBER()OVER(ORDER BY NULL)SOME_ID,UNIFORM(1,2,RANDOM())QTY FROM TABLE(GENERATOR(ROWCOUNT=>10)))
SELECT
TEN_ROWS.*
FROM
TEN_ROWS,LATERAL SPLIT_TO_TABLE(REPEAT('hire me $10/hour',QTY-1),'hire me $10/hour')ALTERNATIVE_APPROACH;
I work in healthcare. In a Postgres database, we have a table member IDs and dates. I'm trying to pull the latest two dates for each member ID.
Simplified sample data:
A 1
B 1
B 2
C 1
C 5
C 7
D 1
D 2
D 3
D 4
Desired result:
A 1
B 1
B 2
C 1
C 5
D 1
D 2
I get a strong feeling this is for a homework assignment and would recommend that you look into partitioning and specifically rank() function by yourself first before looking at my solution.
Moreover, you have not specified how you received the initial result you provided, so I'll have to assume you just did select letter_column, number_column from my_table; to achieve the result.
So, what you actually want here is partition the initial query result into groups by the letter_column and select the first two rows in each. rank() function lets you assign each row a number, counting within groups:
select letter_column,
number_column,
rank() over (partition by letter_column order by number_column) as rank
from my_table;
Since it's a function, you can't use it in a predicate in the same query, so you'll have to build another query around this one, this time filtering the results where rank is over 2:
with ranked_results as (select letter_column,
number_column,
rank() over (partition by letter_column order by number_column asc) as rank
from my_table mt)
select letter_column,
number_column
from ranked_results
where rank < 3;
Here's an SQLFiddle to play around: http://sqlfiddle.com/#!15/e90744/1/0
Hope this helps!
I do have the following table (just a sample) and would like to get the Points subtract from Record2 to Record1. (Record2-Record1) from the latest record of both record1 and 2. The records are entered in category of Match. 1 Match will consists of 2 records which are Record 1 and Record 2.
The output will be 3 as the newest record is ID 3 and 4 from the Match2.)
ID
Name
Points
TimeRecorded
Match
1
Record 1
3
2-Mar 2pm
1
2
Record 2
5
2-Mar 2pm
1
3
Record 1
5
4-Mar 5pm
2
4
Record 2
8
4-Mar 5pm
2
I tried to get the value of subtracting both query as below. But I feel that this is not the good way as it is hard coded for the match and the Name of the record. May I know how to construct a better query in order to get the latest record of the grouped match and calculate the points whereby subtracting Record1 from Record2.
SELECT
(select Points from RunRecord where Name= 'Record2' AND Match = 2)
- (select Points from RunRecord where Name= 'Record1' AND Match = 2)
You could use:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY Name ORDER BY TimeRecorded DESC) rn
FROM yourTable
)
SELECT
MAX(CASE WHEN Name = 'Record 2' THEN Points END) -
MAX(CASE WHEN Name = 'Record 1' THEN Points END) AS diff
FROM cte
WHERE rn = 1;
The CTE assigns a row number for each group of records of the same name, with 1 being assigned to the most recent record. Then, we aggregate over the entire table and pivot out the points to find the difference.
You can use the rank() window function to rank the records by match descending. Then take the top of the ranked records and use conditional aggregation to control the sign of the points added.
SELECT sum(CASE x.name
WHEN 'Record2' THEN
x.points
WHEN 'Record1' THEN
-x.points
END)
FROM (SELECT rr.name,
rr.points,
rank() OVER (ORDER BY rr.match DESC) r
FROM runrecord rr
WHERE name IN ('Record1',
'Record2')) x
WHERE x.r = 1;
I have a query that calculates points based on multiple criteria, and then orders the result set based on those points.
SELECT * FROM (
SELECT
dbo.afunctionthatcalculates(Something, Something) AS Points1
,dbo.anotherone(Something, Something) AS Points2
,dbo.anotherone(Something, Something) AS Points3
,[TotalPoints] = dbo.function(something) + dbo.function(something)
) AS MyData
ORDER BY MyData.TotalPoints
So my first stab at adding placement, rankings.. was this:
SELECT ROW_NUMBER() OVER(MyData.TotalPoints) AS Ranking, * FROM (
SELECT same as above
) AS MyData
ORDER BY MyData.TotalPoints
This adds the Rankings column, but doesn't work when the points are tied.
Rank | TotalPoints
--------------------
1 100
2 90
3 90
4 80
Should be:
Rank | TotalPoints
--------------------
1 100
2 90
2 90
3 80
Not really sure about how to resolve this.
Thank you for your help.
You should use the DENSE_RANK() function which takes the ties into account, as described here: http://msdn.microsoft.com/en-us/library/ms173825.aspx
DENSE_RANK() instead of ROW_NUMBER()
Suppose I have a table:
HH SLOT RN
--------------
1 1 null
1 2 null
1 3 null
--------------
2 1 null
2 2 null
2 3 null
I want to set RN to be a random number between 1 and 10. It's ok for the number to repeat across the entire table, but it's bad to repeat the number within any given HH. E.g.,:
HH SLOT RN_GOOD RN_BAD
--------------------------
1 1 9 3
1 2 4 8
1 3 7 3 <--!!!
--------------------------
2 1 2 1
2 2 4 6
2 3 9 4
This is on Netezza if it makes any difference. This one's being a real headscratcher for me. Thanks in advance!
To get a random number between 1 and the number of rows in the hh, you can use:
select hh, slot, row_number() over (partition by hh order by random()) as rn
from t;
The larger range of values is a bit more challenging. The following calculates a table (called randoms) with numbers and a random position in the same range. It then uses slot to index into the position and pull the random number from the randoms table:
with nums as (
select 1 as n union all select 2 union all select 3 union all select 4 union all select 5 union all
select 6 union all select 7 union all select 8 union all select 9
),
randoms as (
select n, row_number() over (order by random()) as pos
from nums
)
select t.hh, t.slot, hnum.n
from (select hh, randoms.n, randoms.pos
from (select distinct hh
from t
) t cross join
randoms
) hnum join
t
on t.hh = hnum.hh and
t.slot = hnum.pos;
Here is a SQLFiddle that demonstrates this in Postgres, which I assume is close enough to Netezza to have matching syntax.
I am not an expert on SQL, but probably do something like this:
Initialize a counter CNT=1
Create a table such that you sample 1 row randomly from each group and a count of null RN, say C_NULL_RN.
With probability C_NULL_RN/(10-CNT+1) for each row, assign CNT as RN
Increment CNT and go to step 2
Well, I couldn't get a slick solution, so I did a hack:
Created a new integer field called rand_inst.
Assign a random number to each empty slot.
Update rand_inst to be the instance number of that random number within this household. E.g., if I get two 3's, then the second 3 will have rand_inst set to 2.
Update the table to assign a different random number anywhere that rand_inst>1.
Repeat assignment and update until we converge on a solution.
Here's what it looks like. Too lazy to anonymise it, so the names are a little different from my original post:
/* Iterative hack to fill 6 slots with a random number between 1 and 13.
A random number *must not* repeat within a household_id.
*/
update c3_lalfinal a
set a.rand_inst = b.rnum
from (
select household_id
,slot_nbr
,row_number() over (partition by household_id,rnd order by null) as rnum
from c3_lalfinal
) b
where a.household_id = b.household_id
and a.slot_nbr = b.slot_nbr
;
update c3_lalfinal
set rnd = CAST(0.5 + random() * (13-1+1) as INT)
where rand_inst>1
;
/* Repeat until this query returns 0: */
select count(*) from (
select household_id from c3_lalfinal group by 1 having count(distinct(rnd)) <> 6
) x
;