I have a view in a Oracle DB, it looks as follows:
id | type | numrows
----|--------|----------
1 | S | 2
2 | L | 3
3 | S | 2
4 | S | 2
5 | L | 3
6 | S | 2
7 | L | 3
8 | S | 2
9 | L | 3
10 | L | 3
The idea is: if TYPE is 'S' then return 2 rows (randomly), and if TYPE is 'L' then return 3 rows (randomly).
Example:
id | type | numrows
----|--------|----------
1 | S | 2
3 | S | 2
2 | L | 3
5 | L | 3
7 | L | 3
you should tell oracle how to get 3 rows or 2 rows. An ideea is to fabricate a row:
select id, type, numrows
from
(select
id,
type,
numrows,
row_number() over (partition by type order by type) rnk --fabricated
from table)
where
(type = 'S' and rnk <= 2 )
or
(type = 'L' and rnk <= 3 );
You can order by anything you want in that analytic function. For example, you can order by dbms_random.random() for random choices.
If your column numrows is correct and that's the number of rows you want to get then the where clause is simpler:
select id, type, numrows
from
(select
id,
type,
numrows,
row_number() over (partition by type order by dbms_random.random()) rnk --fabricated
from table)
where
rnk <= numrows;
Related
I have a table:
| id | Number |Address
| -----| ------------|-----------
| 1 | 0 | NULL
| 1 | 1 | NULL
| 1 | 2 | 50
| 1 | 3 | NULL
| 2 | 0 | 10
| 3 | 1 | 30
| 3 | 2 | 20
| 3 | 3 | 20
| 4 | 0 | 75
| 4 | 1 | 22
| 4 | 2 | 30
| 5 | 0 | NULL
I need to get: the NUMBER of the last ADDRESS change for each ID.
I wrote this select:
select dh.id, dh.number from table dh where dh =
(select max(min(t.history)) from table t where t.id = dh.id group by t.address)
But this select not correctly handling the case when the address first changed, and then changed to the previous value. For example id=1: group by return:
| Number |
| -------- |
| NULL |
| 50 |
I have been thinking about this select for several days, and I will be happy to receive any help.
You can do this using row_number() -- twice:
select t.id, min(number)
from (select t.*,
row_number() over (partition by id order by number desc) as seqnum1,
row_number() over (partition by id, address order by number desc) as seqnum2
from t
) t
where seqnum1 = seqnum2
group by id;
What this does is enumerate the rows by number in descending order:
Once per id.
Once per id and address.
These values are the same only when the value is 1, which is the most recent address in the data. Then aggregation pulls back the earliest row in this group.
I answered my question myself, if anyone needs it, my solution:
select * from table dh1 where dh1.number = (
select max(x.number)
from (
select
dh2.id, dh2.number, dh2.address, lag(dh2.address) over(order by dh2.number asc) as prev
from table dh2 where dh1.id=dh2.id
) x
where NVL(x.address, 0) <> NVL(x.prev, 0)
);
I have a simple scenario wherein, a table stores data about which card(s) a users uses and if those cards are registered (exist) in the system. I've applied ROW_NUMBER to group them too
SELECT User, CardId, CardExists, ROW_NUMBER() OVER (PARTITION BY User) AS RowNum From dbo.CardsInfo
User | CardID | CardExists | RowNum
-------------------------------------
A | 1 | 0 | 1
A | 2 | 1 | 2
A | 3 | 1 | 3
---------------------------------
B | 4 | 0 | 1
B | 5 | 0 | 2
B | 6 | 0 | 3
B | 7 | 0 | 4
---------------------------------
C | 8 | 1 | 1
C | 9 | 0 | 2
C | 10 | 1 | 3
Now in the above, I need to filter out User cards based on the two rules below
If in the cards registered with a user, multiple cards exist in the system, then take first one. So, for user A, CardID 2 will be returned and for User C it'll return CardID = 8
Othwerwise, if no card is existing (registered) for the user in the system, then just take the first one. So, for user B, it should return CardID = 4
Thus, final returned set should be -
User | CardID | CardExists | RowNum
-------------------------------------
A | 2 | 1 | 2
---------------------------------
B | 4 | 0 | 1
---------------------------------
C | 8 | 1 | 1
How can I do this filteration in SQL?
Thanks
You can use:
SELECT ci.*
FROM (SELECT User, CardId, CardExists,
ROW_NUMBER() OVER (PARTITION BY User ORDER BY CardExists DESC, CardId) AS RowNum
FROM dbo.CardsInfo ci
) ci
WHERE seqnum = 1;
You can also do this with aggregation:
select user,
max(cardexists) as cardexists,
coalesce(min(case when cardexists = 1 then cardid end),
min(card(cardid)
) as cardid
from cardsinfo
group by user;
Or, if you have a separate users table:
select ci.*
from users u cross apply
(select top (1) ci.*
from cardinfo ci
where ci.user = u.user
order by ci.cardexists desc, cardid asc
) ci
Let's say I have a table with the following value
1
1
1
2
2
2
3
3
3
1
1
1
2
2
2
I need to get an out put like this, which counts each occurances of a
particular value
1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3
1 1
1 2
1 3
2 1
2 2
2 3
NB: This is a sample table Actual table is a complex table with lots of rows and columns and query contains some more conditions
If the number repeats over different "islands" then you need to calculate a value to maintain those islands first (grpnum). That first step can be undertaken by subtracting a raw top-to-bottom row number (raw_rownum) from a partitioned row number. That result gives each "island" a reference unique to that island that can then be used to partition a subsequent row number. As each order by can disturb the outcome I find it necessary to use individual steps and to pass the prior calculation up so it may be reused.
SQL Fiddle
MS SQL Server 2014 Schema Setup:
CREATE TABLE Table1 ([num] int);
INSERT INTO Table1 ([num])
VALUES (1),(1),(1),(2),(2),(2),(3),(3),(3),(1),(1),(1),(2),(2),(2);
Query 1:
select
num
, row_number() over(partition by (grpnum + num) order by raw_rownum) rn
, grpnum + num island_num
from (
select
num
, raw_rownum - row_number() over(partition by num order by raw_rownum) grpnum
, raw_rownum
from (
select
num
, row_number() over(order by (select null)) as raw_rownum
from table1
) r
) d
;
Results:
| num | rn | island_num |
|-----|----|------------|
| 1 | 1 | 1 |
| 1 | 2 | 1 |
| 1 | 3 | 1 |
| 2 | 1 | 5 |
| 2 | 2 | 5 |
| 2 | 3 | 5 |
| 1 | 1 | 7 |
| 1 | 2 | 7 |
| 1 | 3 | 7 |
| 3 | 1 | 9 |
| 3 | 2 | 9 |
| 3 | 3 | 9 |
| 2 | 1 | 11 |
| 2 | 2 | 11 |
| 2 | 3 | 11 |
SQL Server provide row_number() function :
select ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY ID) RN FROM <TABLE_NAME>
EDIT :
select * , case when (row_number() over (order by (select 1))) %3 = 0 then 3 else
(row_number() over (order by (select 1))) %3 end [rn] from table
I think there is a problem with your sample, in that you have an implied order but not an explicit one. There is no guarantee that the database will keep and store the values the way you have them listed, so there has to be some inherent/explicit ordering mechanism to tell the database to give those values back exactly the way you listed.
For example, if you did this:
update test
set val = val + 2
where val < 3
You would find your select * no longer comes back the way you expected.
You indicated your actual table was huge, so I assume you have something like this you can use. There should be something in the table to indicate the order you want... a timestamp, perhaps, or maybe a surrogate key.
That said, assuming you have something like that and can leverage it, I believe a series of windowing functions would work.
with rowed as (
select
val,
case
when lag (val, 1, -1) over (order by 1) = val then 0
else 1
end as idx,
row_number() over (order by 1) as rn -- fix this once you have your order
from
test
),
partitioned as (
select
val, rn,
sum (idx) over (order by rn) as instance
from rowed
)
select
val, instance, count (1) over (partition by instance order by rn)
from
partitioned
This example orders by the way they are listed in the database, but you would want to change the row_number function to accommodate whatever your real ordering mechanism is.
1 1 1
1 1 2
1 1 3
2 2 1
2 2 2
2 2 3
3 3 1
3 3 2
3 3 3
1 4 1
1 4 2
1 4 3
2 5 1
2 5 2
2 5 3
Both of these tables already exist, so not looking for a dynamic situation. The goal is to consolidate the data rows horizontally, but have them to the leftmost "data" field available. There will never be a 4th entry.
I am using Microsoft SQL Server
Table1:
ID|Data
--------
A | 1
A | 2
B | 3
C | 4
C | 5
C | 6
Table2:
ID | Data 1 | Data 2 | Data 3
------------------------------
A | | |
B | | |
C | | |
Desired Result of Table2:
ID | Data 1 | Data 2 | Data 3
------------------------------
A | 1 | 2 |
B | 3 | |
C | 6 | 7 | 8
You can use row_number:
select id,
max(case when rn = 1 then data end) as data_1,
max(case when rn = 2 then data end) as data_2,
max(case when rn = 3 then data end) as data_3
from (
select t.*,
row_number() over (
partition by id order by data
) as rn
from your_table t
) t
group by id;
I have a table with data like the following
key | A | B | C
---------------------------
1 | x | 0 | 1
2 | x | 2 | 0
3 | x | NULL | 4
4 | y | 7 | 1
5 | y | 3 | NULL
6 | z | NULL | 4
And I want to merge the rows together based on column A with largest primary key being the 'tie breaker' between values that are not NULL
Result
key | A | B | C
---------------------------
1 | x | 2 | 4
2 | y | 3 | 1
3 | z | NULL | 4
What would be the best way to achieve this assuming my data is actually 40 columns and 1 million rows with an unknown level of duplications?
Using ROW_NUMBER and conditional aggregation:
SQL Fiddle
WITH cte AS(
SELECT *,
rnB = ROW_NUMBER() OVER(PARTITION BY A ORDER BY CASE WHEN B IS NULL THEN 0 ELSE 1 END DESC, [key] DESC),
rnC = ROW_NUMBER() OVER(PARTITION BY A ORDER BY CASE WHEN C IS NULL THEN 0 ELSE 1 END DESC, [key] DESC)
FROM tbl
)
SELECT
[key] = ROW_NUMBER() OVER(ORDER BY A),
A,
B = MAX(CASE WHEN rnB = 1 THEN B END),
C = MAX(CASE WHEN rnC = 1 THEN C END)
FROM cte
GROUP BY A