Hi guys i have a postgres table with a column for event and a column for sequence. Every event may have multiple sequences. For ex:
Event | Sequence
a | 1
a | 4
a | 5
b | 1
b | 2
Now i know that select min(sequence) group by event gives me the minimum sequence. How do i get the very next value after the min value. i hope that makes sense. Thanks in advance.
I'm Using Postgres 9.3.
You can use ROW_NUMBER() partitioning by Event and ordering by Sequence to get the second lowest sequence number per Event;
SELECT Event, Sequence
FROM (
SELECT Event, Sequence,
ROW_NUMBER() OVER (PARTITION BY Event ORDER BY Sequence) rn
FROM Table1
) z
WHERE rn = 2;
An SQLfiddle to test with.
EDIT A bit more complicated, but if you need a query that doesn't rely on ROW_NUMBER(), use a subquery with a self-join to exclude rows with minimum sequence for each event:
SELECT outer_query.Event, MIN(outer_query.Sequence) AS SecondMinSeq
FROM Table1 as outer_query
INNER JOIN (
SELECT Table1.Event, MIN(Sequence) AS MinSeq
FROM Table1
GROUP BY Table1.Event
) AS min_sequences
ON outer_query.Event = min_sequences.Event AND outer_query.Sequence <> min_sequences.MinSeq
GROUP BY outer_query.Event
SQL Fiddle: http://sqlfiddle.com/#!15/4438b/7
Related
I'm looking for an efficient approach where I can assign numbers in sequence to each group.
Record Group GroupSequence
-------|---------|--------------
1 Car 1
2 Car 2
3 Bike 1
4 Bus 1
5 Bus 2
6 Bus 3
I came through this question: How to add sequence number for groups in a SQL query without temp tables. But my use case is slightly different from it. Any ideas on how to accomplish this with a single query?
You are looking for row_number():
select t.*, row_number() over (partition by group order by record) as group_sequence
from t;
You can calculate this when you need it, so I see no reason to store it. However, you can update the values if you like:
update t
set group_sequence = tt.new_group_sequence
from (select t.*,
row_number() over (partition by group order by record) as new_group_sequence
from t
) tt
where tt.record = t.record;
i've got a table that i need to return about 14 column values but only return 1 row for the duplicates on some of the columns.
The second problem is that between the duplicates i need to keep the one that has the biggest int in one of the columns that is not required to be unique.
Since the Table is somewhat big, I am seeking advice into doing this in the most efficient way.
should i be doing a group by?
my table is somewhat like this, i will simplify the number of columns.
ID(UniqueIdentifier) | ACCID(UniqueIdentifier) | DateTime(DateTime) | distance(int)|type(int)
28761188-0886-E911-822F-DD1FA635D450 1238FD8A-BD00-411A-A81C-0F6F5C026BCC 2019-06-03 14:04:41.000 2 3
41761188-0886-E911-822F-DD1FA635D450 1238FD8A-BD00-411A-A81C-0F6F5C026BCC 2019-06-03 14:04:41.000 1 3
I should be only selecting when ACCID and DATETIME is unique, the column ID in primary so will never be duplicate, and i need to keep the row with the biggest distance.
You can use the ROW_NUMBER() window function, as in:
select *
from (
select
id,
accid,
datetime,
distance,
type,
row_number() over(partition by accid, datetime order by type desc) as rn
from t
) x
where rn = 1
If you want to show multiple "ties", then replace ROW_NUMBER() by RANK().
I would suggest a correlated subquery with the right index as the fastest method:
select t.*
from t
where t.id = (select top (1) t2.id
from t t2
where t2.ACCID = t.ACCID
order by t2.distance desc
) ;
The best index is on (ACCID, distance desc, id).
I have a table 'TEST' as shown below
Number | Seq | Name
-------+-------+------
123 | 1 | Hello
123 | 2 | Hi
123 | 3 | Greetings
234 | 1 | Goodbye
234 | 2 | Bye
I want to write a query, to group the table by 'Number', and select the rows with the maximum sequence number (MAX(Seq)). The output of the query would be
Number | Seq | Name
-------+-------+------
123 | 3 | Greetings
234 | 2 | Bye
How do I go about this?
EDIT: TEST is actually a table that is the result from a long query (joining multiple tables) that I have already written. I already have a (SELECT ...) statement to get the values I need. Is there a way to remove duplicate rows (with the same 'Number' as shown above) and select only the one with maximum 'Seq' value.
I am on Microsoft SQL Server 2008 (SP2)
I was hoping there would be a way to achieve this by
SELECT * FROM (SELECT ...) TEST <condition to group>
You can use a select win in clause
select * from test
where (number, count) in (select number, max(count) from test group by Number)
Another option is to use a windowed ROW_NUMBER() function with a partition on the number:
With Cte As
(
Select *,
Row_Number() Over (Partition By Number Order By Count Desc) RN
From TEST
)
Select Number, Count, Name
From Cte
Where RN = 1
SELECT *
FROM (SELECT test.*, MAX (seq) OVER (PARTITION BY num) max_seq
FROM test)
WHERE seq = max_seq
I changed the column name from number because you can't use a reserved word for a column name. This is pretty much the same as the other answers, except that it explicitly gets the maximum sequence number for each NUM.
You want to use an ANALYTIC function together with a conditional clause to get you only the rows of TEST that you desire.
WITH TEST as (
...your really complex query that generates TEST...
)
SELECT
Number, Seq, Name,
RANK() OVER (PARTITION By Number ORDER BY Seq DESC) AS aRank
FROM Test
WHERE aRank = 1
;
This returns the Number, Seq, Name for each Number grouping where the Seq is maximum. Yes, it also returns a column named aRank with all '1' in it...hopefully it can be ignored.
The solution to this is to do an self join on only the MAX(Seq) values.
This answer can be found at SQL Select only rows with Max Value on a Column
Let's say I have a table with two columns:
id | value
----------
1 | 101
2 | 356
3 | 28
I need to randomly permute the value column so that each id is randomly assigned a new value from the existing set {101,356,28}. How could I do this in Oracle SQL?
It may sound odd but this is a real problem, just with more columns.
You can do this by using row_number() with a random number generator and then joining back to the original rows:
with cte as (
select id, value,
row_number() over (order by id) as i,
row_number() over (order by dbms_random.random) as rand_i
from table t
)
select cte.id, cte1.value
from cte join
cte cte1
on cte.i = cte.rand_i;
This guarantees a permutation (i.e. no original row has its value used twice).
EDIT:
By the way, if the original ids are sequential from 1 and have no gaps, you could just do:
select row_number() over (order by dbms.random) as id, value
from table t;
An Option : select * from x_table where id = round(dbms_random.value() * 3) + 1; [Here 3 is the number of rows in your random data table and I am assuming that id is incremental and unique?]
I'll think of other options.
I'm not sure whether this is the right task for SQL database. Maybe you should implement something like this:
Factoradic permutation - in PL/SQL and then return a cursor via PIPE ROW construct. Ordering by dbms.random might be slow for large data sets.
I am working on SQL Server. I have a table, that contains around 75000 records. Among them there are several duplicate records. So i wrote a query to know which record repeated how many times like,
SELECT [RETAILERNAME],COUNT([RETAILERNAME]) as Repeated FROM [Stores] GROUP BY [RETAILERNAME]
It gives me result like,
---------------------------
RETAILERNAME | Repeated
---------------------------
X | 4
---------------------------
Y | 6
---------------------------
Z | 10
---------------------------
Among 4 record(s) of X record, i need take only first record of X.
so here i want to retrieve all fields from first row of duplicate records. i.e. Take all records whose RETAILERNAME='X' we will get some no. of duplicate records, we need to get only first row from them.
Please guide me.
You could try using ROW_NUMBER.
Something like
;WITH Vals AS (
SELECT [RETAILERNAME],
ROW_NUMBER() OVER(PARTITION BY [RETAILERNAME] ORDER BY [RETAILERNAME]) RowID
FROM [Stores ]
)
SELECT *
FROm Vals
WHERE RowID = 1
SQL Fiddle DEMO
You can then also remove the duplicates if need be (BUT BE CAREFUL THIS IS PERMANENT)
;WITH Vals AS (
SELECT [RETAILERNAME],
ROW_NUMBER() OVER(PARTITION BY [RETAILERNAME] ORDER BY [RETAILERNAME]) RowID
FROM Stores
)
DELETE
FROM Vals
WHERE RowID > 1;
You Can write query as under
SELECT TOP 1 * FROM [Stores] GROUP BY [RETAILERNAME]
HAVING your condition
WITH cte
AS (SELECT [retailername],
Row_number()
OVER(
partition BY [retailername]
ORDER BY [retailername])'RowRank'
FROM [retailername])
SELECT *
FROM cte