Can I rewrite this select without using aggregate function to retrieve the highest value
Select *
From A
Where Id= 123
and value = (
select max(value)
from A inner
where inner.id = 123 )
If you are certain that only one record would have the max value, or, if there are ties you don't care which gets returned, then you may use this limit query:
SELECT *
FROM A
WHERE Id = 123
ORDER BY value DESC
LIMIT 1;
If this doesn't meet your expectations, then stick with your current approach. Note that you could also use RANK() here:
WITH cte AS (
SELECT *, RANK() OVER (ORDER BY value DESC) rnk
FROM A
WHERE Id = 123
)
SELECT *
FROM cte
WHERE rnk = 1;
But like your version, the above rank query also requires a subquery.
Related
I am trying to dedupe my dataset using rank, but it is not assigning a different number to the second record. What am I doing wrong here?
with get_rank as (
select id, code, rank() over (partition by id order by z.rowid) as ranking
from mytable z
)
select *
from get_rank
where ranking = 1
and id = 72755
ID CODE RANKING
---------- ---- ----------
72755 M 1
72755 M 1
Use row_number():
with get_rank as (
select id, code,
row_number() over (partition by id order by z.rowid) as ranking
from mytable z
)
select *
from get_rank
where ranking = 1 and id = 72755;
It is guaranteed to return a different value for each row.
Group by the highest Number in a column worked great with MAX(), but what if I would like to get the cell that is at most common.
As example:
ID
100
250
250
300
200
250
So I would like to group by ID and instead of get the lowest (MIN) or highest (MAX) number, I would like to get the most common one (that would be 250, because there 3x).
Is there an easy way in SQL Server 2012 or am I forced to add a second SELECT where I COUNT(DISTINCT ID) and add that somehow to my first SELECT statement?
You can use dense_rank to return all the id's with the highest counts. This would handle cases when there are ties for the highest counts as well.
select id from
(select id, dense_rank() over(order by count(*) desc) as rnk from tablename group by id) t
where rnk = 1
A simple way to do what you want uses top and order by:
SELECT top 1 id
FROM t
GROUP BY id
ORDER BY COUNT(*) DESC;
This is a statistic called the mode. Getting the mode and max is a bit challenging in SQL Server. I would approach it as:
WITH cte AS (
SELECT t.id, COUNT(*) AS cnt,
row_number() OVER (ORDER BY COUNT(*) DESC) AS seqnum
FROM t
GROUP BY id
)
SELECT MAX(id) AS themax, MAX(CASE WHEN seqnum = 1 THEN id END) AS MODE
FROM cte;
why below query is not giving results if I remove the < sign from query.Because even without < it must match with results?
Query used to get second max id value:
select min(id)
from(
select distinct id
from student
order by id desc
)
where rownum <=2
student id
1
2
3
4
Rownum has a special meaning in Oracle. It is increased with every row, but the optimizer knows that is increasing continuously and all consecutive rows must met the rownum condition. So if you specify rownum = 2 it will never occur since the first row is already rejected.
You can see this very nice if you do an explain plan on your query. It will show something like:
Plan for rownum <=:
COUNT STOPKEY
Plan for rownum =:
FILTER
A ROWNUM value is not assigned permanently to a row (this is a common misconception). A row in a table does not have a number; you cannot ask for row 2 or 3 from a table
click Here for more Info.
This is from the link provided:
Also confusing to many people is when a ROWNUM value is actually assigned. A ROWNUM value is assigned to a row after it passes the predicate phase of the query but before the query does any sorting or aggregation. Also, a ROWNUM value is incremented only after it is assigned, which is why the following query will never return a row:
select *
from t
where ROWNUM > 1;
Because ROWNUM > 1 is not true for the first row, ROWNUM does not advance to 2. Hence, no ROWNUM value ever gets to be greater than 1. Consider a query with this structure:
select ..., ROWNUM
from t
where <where clause>
group by <columns>
having <having clause>
order by <columns>;
I think this is the query you are looking for:
select id
from (select distinct id
from student
order by id desc
) t
where rownum <= 2;
Oracle processes the rownum before the order by, so you need a subquery to get the first two rows. The min() was forcing an aggregation that returned only one result, but before the rownum was applied.
If you actually want only the second value, you need an additional layer of subqueries:
select min(id)
from (select id
from (select distinct id
from student
order by id desc
) t
where rownum <= 2
) t;
However, I would do:
select id
from (select id, dense_rank() over (order by id) as seqnum
from student
) t
where seqnum = 2;
Order asc instead of desc
select id from student where rownum <=2 order by id asc;
Why not just use
select id
from ( select distinct id
, row_number() over (order by id desc) x
from student
)
where x = 2
Or even really bad. Getting the count and index :)
select id
from ( select id
, row_number() over (order by id desc) idx
, sum(1) over (order by null) cnt
from student
group
by id
)
where idx = cnt - 1 -- get the pre-last
Or
where idx = cnt - 2 -- get the 2nd-last
Or
where idx = 3 -- get the 3rd
Try this
SELECT *
FROM (
SELECT id, row_number() over (order by id asc) row_num
FROM student
) AS T
WHERE row_num = 2 -- or 3 ... n
ROW_NUMBER
I have the follow sql statement. I'm trying to get the highest version. My query is returning multiple results, although sorted by verison desc. How can I just get the highest one?
SELECT pv.version, pv.vin, pv.policyid, pv.segeffdate, pv.segexpdate, pv.changenum from
nsa_al.polvehicle pv
WHERE pv.vin = '2GTEC19T011201788'
AND pv.changenum > 0
AND pv.VERSION = (SELECT MAX(PV.VERSION) FROM NSA_AL.POLVERSION)
ORDER BY pv.version DESC
I've tried to use the rownum = 1 but I kept getting missing ")" error.
Thanks
There are a couple of ways to do this. Here is one with a subquery and ROWNUM:
SELECT *
FROM (
SELECT pv.version, pv.vin, pv.policyid, pv.segeffdate, pv.segexpdate, pv.changenum
FROM nsa_al.polvehicle pv
WHERE pv.vin = '2GTEC19T011201788'
AND pv.changenum > 0
ORDER BY pv.version DESC
) t
WHERE ROWNUM = 1
SQL Fiddle Demo
This will only return a single record. If you need ties, you can use the analytic function RANK() instead.
SELECT *
FROM (
SELECT RANK() OVER (ORDER BY version DESC) rnk, pv.version, pv.vin, pv.changenum
FROM pv
WHERE pv.vin = '2GTEC19T011201788'
AND pv.changenum > 0
ORDER BY pv.version DESC
) t
WHERE rnk = 1
If you prefer to use a MAX aggregate, then it's easiest to do that with a common table expression and JOIN the table back on itself. This could yield multiple results if there are multiple records with the same version:
WITH CTE AS (
SELECT pv.version, pv.vin, pv.changenum
FROM pv
WHERE pv.vin = '2GTEC19T011201788'
AND pv.changenum > 0
)
SELECT *
FROM CTE C
JOIN (
SELECT MAX(version) maxVersion
FROM CTE) C2 ON C.version = C2.maxVersion
More Fiddle
I'm trying to set ROW_NUMBER()... as an alias so I can reference it in the OFFSET. e.g. OFFSET some_alias - 1. I need to get a single row including the ROW_NUMBER() from a larger query. Here's my working code (gets correct ROW_NUMBER(), but isn't offset by the right amount):
WITH FirstQuery AS (
SELECT "RepInitials", COUNT("OrderStatus"), ROW_NUMBER()OVER(ORDER BY COUNT("OrderStatus") DESC)
FROM "tblBulkSalesQuery"
WHERE "OrderStatus" = 'CMC'
GROUP BY "RepInitials"
)
SELECT "RepInitials", COUNT("OrderStatus"), ROW_NUMBER()OVER(ORDER BY COUNT("OrderStatus") DESC)
FROM "tblBulkSalesQuery"
WHERE "OrderStatus" = 'CMC'
GROUP BY "RepInitials"
LIMIT 1
OFFSET 1;
select *
from (
SELECT "RepInitials",
COUNT("OrderStatus") as order_status_count,
ROW_NUMBER() OVER (ORDER BY COUNT("OrderStatus") DESC) as rn
FROM "tblBulkSalesQuery"
WHERE "OrderStatus" = 'CMC'
GROUP BY "RepInitials"
) as t
where rn = 1
Edit:
The t is an alias for the nested select ("derived table"). PostgreSQL requires each derived table to get it's own "name" and that can only be done by assigning a alias.
It's pretty much the same as:
with t as (
... here goes the real select ...
)
select *
from t
where rn = 1;