Consider this data (View on DB Fiddle):
id
dept
value
1
A
5
1
A
5
1
B
7
1
C
5
2
A
5
2
A
5
2
B
15
2
A
2
The base query I am running is pretty simple. Just get the total value by id and the most frequent dept.
SELECT
id,
MODE() WITHIN GROUP(ORDER BY dept) AS dept_freq,
SUM(value) AS value
FROM test
GROUP BY id
;
id
dept_freq
value
1
A
22
2
A
27
But I also need to get, for each id, the dept that concentrates the greatest value (so the greatest sum of value by id and dept, not the highest individual value in the original table).
Is there any way to use window functions to achieve that and do it directly in the base query above?
The expected output for this particular example would be:
id
dept_freq
dept_value
value
1
A
A
22
2
A
B
27
I could achieve that with the query below and then joining that with the results of the base query above
SELECT * FROM(
SELECT
*,
ROW_NUMBER() OVER(PARTITION BY id ORDER BY value DESC) as row
FROM (
SELECT id, dept, SUM(value) AS value
FROM test
GROUP BY id, dept
) AS alias1
) AS alias2
WHERE alias2.row = 1
;
id
dept
value
row
1
A
10
1
2
B
15
1
But it is not easy to read/maintain and seems also pretty inefficient. So I thought it should be possible to achieve this using window functions directly in the base query, and that also may also help Postgres to come up with a better query plan that does less passes over the data. But none of my attempts using over partition and filter worked.
step-by-step demo:db<>fiddle
You can fetch the dept for the highest values using the first_value() partition function. Adding this before your mode() grouping should do it:
SELECT
id,
highest_value_dept,
MODE() WITHIN GROUP(ORDER BY dept) AS dept_freq,
SUM(value) as value
FROM (
SELECT
id,
dept,
value,
FIRST_VALUE(dept) OVER (PARTITION BY id ORDER BY value DESC) as highest_value_dept
FROM test
) s
GROUP BY 1,2
Related
I have a table format like below:
Id Code
1 A
1 B
2 A
3 A
3 C
4 A
4 B
I am trying to get count of code combinations like below:
Code Count
A,B 2 -- Row 1,2 and Row 6,7
A 1 -- Row 3
A,C 1 -- Row 4
I am unable to get the combination result. All I can do is group by but I am not getting count of IDs based in combinations.
You need to aggregate the rows, somehow, and do that twice. The code looks something like this:
select codes, count(*) as num_ids
from (select id, group_concat(code order by code) as codes
from t
group by id
) id
group by code;
group_concat() might be spelled listagg() or string_agg() depending on the database.
In SQL Server, use string_agg():
select codes, count(*) as num_ids
from (select id, string_agg(code, ',') within group (order by code) as codes
from t
group by id
) id
group by code;
Please help me t make below select query
Source table
name Amount
-----------
A 2
B 3
C 2
D 7
if limit is 5 then result table should be
name Amount
-----------
A 2
B 3
if limit is 8 then result table
name Amount
-----------
A 2
B 3
C 2
You can use window function to achieve this:
select name,
amount
from (
select t.*,
sum(amount) over (
order by name
) s
from your_table t
) t
where s <= 8;
The analytic function sum will be aggregated row-by-row based on the given order order by name.
Once you found sum till given row using this, you can filter the result using a simple where clause to find rows till which sum of amount is under or equal to the given limit.
More on this topic:
The SQL OVER() clause - when and why is it useful?
https://explainextended.com/2009/03/08/analytic-functions-sum-avg-row_number/
Does anyone happen to know a way of basically taking the 'Distinct' command but only using it on a single column. For lack of example, something similar to this:
Select (Distinct ID), Name, Term from Table
So it would get rid of row with duplicate ID's but still use the other column information. I would use distinct on the full query but the rows are all different due to certain columns data set. And I would need to output only the top most term between the two duplicates:
ID Name Term
1 Suzy A
1 Suzy B
2 John A
2 John B
3 Pete A
4 Carl A
5 Sally B
Any suggestions would be helpful.
select t.Id, t.Name, t.Term
from (select distinct ID from Table order by id, term) t
You can use row number for this
Select ID, Name, Term from(
Select ID, Name, Term, ROW_NUMBER ( )
OVER ( PARTITION BY ID order by Name) as rn from Table
Where rn = 1)
as tbl
Order by determines the order from which the first row will be picked.
ID Sum Name
a 10 Joe
a 8 Mary
b 21 Kate
b 110 Casey
b 67 Pierce
What would you recommend as the best way to
obtain for each ID the name that corresponds to the largest sum (grouping by ID).
What I tried so far:
select ID, SUM(Sum) s, Name
from Table1
group by ID, Name
Order by SUM(Sum) DESC;
this will arrange the records into groups that have the highest sum first. Then I have to somehow flag those records and keep only those. Any tips or pointers? Thanks a lot
In the end I'd like to obtain:
a 10 Joe
b 110 Casey
You want the row_number() function:
select id, [sum], name
from (select t.*]
row_number() over (partition by id order by [sum] desc) as seqnum
from table1
) t
where seqnum = 1;
Your question is more confusing than it needs to be because you have a column called sum. You should avoid using SQL reserved words for identifiers.
The row_number() function assigns a sequential number to a group of rows, starting with 1. The group is defined by the partition by clause. In this case, all rows with the same id are in the same group. The ordering of the numbers is determined by the order by clause, so the one with the largest value of sum gets the value of 1.
If you might have duplicate maximum values and you want all of them, use the related function rank() or dense_rank().
select *
from
(
select *
,rn = row_number() over (partition by Id order by sum desc)
from table
)x
where x.rn=1
demo
Suppose I have a table filled with the data below, what SQL function or query I should use in db2 to retrieve all rows having the FIRST field FLD_A with value A, the FIRST field FLD_A with value B..and so on?
ID FLD_A FLD_B
1 A 10
2 A 20
3 A 30
4 B 10
5 A 20
6 C 30
I am expecting a table like below; I am aware of grouping done by function GROUP BY but how can I limit the query to return the very first of each group?
Essentially I would like to have the information about the very first row where a new value for FLD_A is appearing for the first time?
ID FLD_A FLD_B
1 A 10
4 B 10
6 C 30
Try this it works in sql
SELECT * FROM Table1
WHERE ID IN (SELECT MIN(ID) FROM Table1 GROUP BY FLD_A)
A good way to approach this problem is with window functions and row_number() in particular:
select t.*
from (select t.*,
row_number() over (partition by fld_a order by id) as seqnum
from table1
) t
where seqnum = 1;
(This is assuming that "first" means "minimum id".)
If you use t.*, this will add one extra column to the output. You can just list the columns you want to avoid this.