How to fetch every 10th row from a table i.e. 10th,20th etc. But if there are less than 10 rows in that table, It should fetch the last row.
This can be an advance form of this query present in this question -
How can I select 10th, 20th, 30th ... row of the result of another select query
I have done something like this for selecting every 10th row -
select case_id
from
(select case_id,rownum as seq
from table
where from = 'A' and to ='B'
order by ID
)
where mod(seq,10) = 0
But if there are less than 10 rows in the result of inner query, It should fetch the last row.
OBS: database - Oracle 12c
SELECT ColumnA,
ColumnB,
ColumnC
FROM (
SELECT ROWNUM rn,
COUNT(*) OVER ( ORDER BY NULL ) mx,
q.ColumnA,
q.ColumnB,
q.ColumnC
FROM (
SELECT ColumnA,
ColumnB,
ColumnC
FROM your_table
ORDER BY ColumnA
) q
)
WHERE MOD( rn, 10 ) = 0
OR ( mx = rn AND mx < 10 );
Related
Given a table of IDs in an Oracle database, what is the best method to randomly flag (x) percent of them? In the example below, I am randomly flagging 20% of all records.
ID ELIG
1 0
2 0
3 0
4 1
5 0
My current approach shown below works fine, but I am wondering if there is a more efficient way to do this?
WITH DAT
AS ( SELECT LEVEL AS "ID"
FROM DUAL
CONNECT BY LEVEL <= 5),
TICKETS
AS (SELECT "ID", 1 AS "ELIG"
FROM ( SELECT *
FROM DAT
ORDER BY DBMS_RANDOM.VALUE ())
WHERE ROWNUM <= (SELECT ROUND (COUNT (*) / 5, 0) FROM DAT)),
RAFFLE
AS (SELECT "ID", 0 AS "ELIG"
FROM DAT
WHERE "ID" NOT IN (SELECT "ID"
FROM TICKETS)
UNION
SELECT * FROM TICKETS)
SELECT *
FROM RAFFLE;
You could use a ROW_NUMBER approach here:
WITH cte AS (
SELECT t.*, ROW_NUMBER() OVER (ORDER BY dbms_random.value) rn,
COUNT(*) OVER () cnt
FROM yourTable t
)
SELECT t.*,
CASE WHEN rn / cnt <= 0.2 THEN 'FLAG' END AS flag -- 0.2 to flag 20%
FROM cte t
ORDER BY ID;
Demo
Sample output for one run of the above query:
Note that one of five records is flagged, which is 20%.
I have a Oracle table with the following columns
Table Structure
In a query I need to return all the records with CPER>=40 which is trivial. However, apart from CPER>=40 I need to list 5 random records for each CPID.
I have attached a sample list of records. However, in my table I have around 50,000 records.
Appreciate if you can help.
Oracle solution:
with CTE as
(
select t1.*,
row_number() over(order by DBMS_RANDOM.VALUE) as rn -- random order assigned
from MyTable t1
where CPID <40
)
select *
from CTE
where rn <=5 -- pick 5 at random
union all
select t2.*, null
from my_table t2
where CPID >= 40
SQL Server:
with CTE as
(
select t1.*,
row_number() over(order by newid()) as rn -- random order assigned
from MyTable t1
where CPID <40
)
select *
from CTE
where rn <=5 -- pick 5 at random
union all
select t2.*, null
from my_table t2
where CPID >= 40
How about something like this...
SELECT *
FROM (SELECT CID,
CVAL,
CPID,
CPER,
Row_number() OVER (partition BY CPID ORDER BY CPID ASC ) AS RN
FROM Table) tmp
WHERE CPER>=40 OR pids <= 5
However, this is not random.
Assuming that you want five additional random records, you can do:
select t.*
from (select t.*,
row_number() over (partition by cpid,
(case when cper >= 40 then 1 else 2 end)
order by dbms_random.value
) as seqnum
from t
) t
where seqnum <= 5 or cper >= 40;
The row_number() is enumerating the rows for each cpid in two groups -- based on the cper value. The outer where is taking all cper values in the range you want as well as five from the other group.
There are 25 records in this sql query
I want to get between 5 and 10. How can I do it ?
I use 11g
select
(
select count(*) as sayfasayisi
from konular t
where t.kategori is not null
) as sayfasayisi,
t.id,
t.uye,
t.baslik,t.mesaj,t.kategori,t.tarih,
t.edittarih,t.aktif,t.indirimpuani,t.altkategori,t.link,
nvl(
(select case when t.id = f.konuid and f.uye = 'test' then '1' else '0' end
from takipkonu f where t.id = f.konuid and f.uye = 'test'), '0') as takip
from konular t
where t.kategori is not null
You can use ROW_NUMBER() to assign a row number based on some ordering logic contained in your current query, e.g. a certain column. Then, retain only the 5th to 10th records:
select t.*
from
(
select
(
select count(*) as sayfasayisi
from konular t
where t.kategori is not null
) as sayfasayisi,
ROW_NUMBER() OVER (ORDER BY some_col) rn,
t.id,
t.uye,
...
) t
where t.rn between 5 and 10;
I am trying to write a procedure that inserts calculated table data into another table.
The problem I have is that I need each row's calculated column to be influenced by the result of the previous row's calculated column. I tried to lag the calculation itself but this does not work!
Such as:
(Max is a function I created that returns the highest of two values)
Id Product Model Column1 Column2
1 A 1 5 =MAX(Column1*2, Lag(Column2))
2 A 2 2 =MAX(Column1*2, Lag(Column2))
3 B 1 3 =MAX(Column1*2, Lag(Column2))
If I try the above in SQL:
SELECT
Column1,
MyMAX(Column1,LAG(Column2, 1, 0) OVER (PARTITION BY Product ORDER BY Model ASC) As Column2
FROM Source
...it says column2 is unknown.
Output I get if I LAG the Column2 calculation:
Select Column1, MyMAX(Column1,LAG(Column1*2, 1, 0) OVER (PARTITION BY Product ORDER BY Model ASC) As Column2
Id Column1 Column2
1 5 10
2 2 10
3 3 6
Why 6 on row 3? Because 3*2 > 2*2.
Output that I want:
Id Column1 Column2
1 5 10
2 2 10
3 3 10
Why 10 on row 3? Because previous result of 10 > 3*2
The problem is I can't lag the result of Column2 - I can only lag other columns or calculations of them!
Is there a technique of achieving this with LAG or must I use Recursive CTE? I read that LAG succeeds CTE so I assumed it would be possible. If not, what would this 'CTE' look like?
Edit: Or alternatively - what else could I do to resolve this calculation?
Edit
In hindsight, this problem is a running partitioned maximum over Column1 * 2. It can be done as simply as
SELECT Id, Column1, Model, Product,
MAX(Column1 * 2) OVER (Partition BY Model, Product Order BY ID ASC) AS Column2
FROM Table1;
Fiddle
Original Answer
Here's a way to do this with a recursive CTE, without LAG at all, by joining on incrementing row numbers. I haven't assumed that your Id is contiguous, hence have added an additional ROW_NUMBER(). You haven't mentioned any partitioning, so haven't applied same. The query simply starts at the first row, and then projects the greater of the current Column1 * 2, or the preceding Column2
WITH IncrementingRowNums AS
(
SELECT Id, Column1, Column1 * 2 AS Column2,
ROW_NUMBER() OVER (Order BY ID ASC) AS RowNum
FROM Table1
),
lagged AS
(
SELECT Id, Column1, Column2, RowNum
FROM IncrementingRowNums
WHERE RowNum = 1
UNION ALL
SELECT i.Id, i.Column1,
CASE WHEN (i.Column2 > l.Column2)
THEN i.Column2
ELSE l.Column2
END,
i.RowNum
FROM IncrementingRowNums i
INNER JOIN lagged l
ON i.RowNum = l.RowNum + 1
)
SELECT Id, Column1, Column2
FROM lagged;
SqlFiddle here
Edit, Re Partitions
Partitioning is much the same, by just dragging the Model + Product columns through, then partitioning by these in the row numbering (i.e. starting back at 1 each time the Product or Model resets), including these in the CTE JOIN condition and also in the final ordering.
WITH IncrementingRowNums AS
(
SELECT Id, Column1, Column1 * 2 AS Column2, Model, Product,
ROW_NUMBER() OVER (Partition BY Model, Product Order BY ID ASC) AS RowNum
FROM Table1
),
lagged AS
(
SELECT Id, Column1, Column2, Model, Product, RowNum
FROM IncrementingRowNums
WHERE RowNum = 1
UNION ALL
SELECT i.Id, i.Column1,
CASE WHEN (i.Column2 > l.Column2)
THEN i.Column2
ELSE l.Column2
END,
i.Model, i.Product,
i.RowNum
FROM IncrementingRowNums i
INNER JOIN lagged l
ON i.RowNum = l.RowNum + 1
AND i.Model = l.Model AND i.Product = l.Product
)
SELECT Id, Column1, Column2, Model, Product
FROM lagged
ORDER BY Model, Product, Id;
Updated Fiddle
I need to do a query to return the next (or prev) record if a certain record is not present. For instance consider the following table:
ID (primary key) value
1 John
3 Bob
9 Mike
10 Tom.
I'd like to query a record that has id 7 or greater if 7 is not present.
My questions are,
Are these type of queries possible with SQL?
What are such queries called in the DB world?
Thanks!
Yes, it's possible, but implementation will depend on your RDBMS.
Here's what it looks like in MySQL, PostgreSQL and SQLite:
select ID, value
from YourTable
where id >= 7
order by id
limit 1
In MS SQL-Server, Sybase and MS-Access:
select top 1 ID, value
from YourTable
where id >= 7
order by id
In Oracle:
select * from (
select ID, value
from YourTable
where id >= 7
order by id
)
where rownum = 1
In Firebird and Informix:
select first 1 ID, value
from YourTable
where id >= 7
order by id
In DB/2 (this syntax is in SQL-2008 standard):
select id, value
from YourTable
where id >= 7
order by id
fetch first 1 rows only
In those RDBMS that have "window" functions (in SQL-2003 standard):
select ID, Value
from (
select
ROW_NUMBER() OVER (ORDER BY id) as rownumber,
Id, Value
from YourTable
where id >= 7
) as tmp --- remove the "as" for Oracle
where rownumber = 1
And if you are not sure which RDBMS you have:
select ID, value
from YourTable
where id =
( select min(id)
from YourTable
where id >= 7
)
Try this for MS-SQL:
SELECT TOP 1
id, value
FROM your_table
WHERE id >= 7
ORDER BY id
or for MySql
SELECT id, value
FROM your_table
WHERE id >= 7
ORDER BY id
LIMIT 0,1
I would simply do it like this:
select top 1 * from myTable where id >=7
order by id
implementation of the top 1 part is T-SQL (MSSQL/Sybase), other implementations vary but it is always possible (mysql/postgre LIMIT 1, oracle rownum = 1)
select top 1 * from Persons where Id >= #Id order by Id