I have a table with columns:
ID | FULLNAME | VALUE
01 Joseph 10
02 Sam 50
... ... ...
I need to select row with maximum value, and show info like
FULLNAME | VALUE
I tried using group function MAX(), but I can't select fullname, because if I use it as a GROUP BY expression, it will select max in groups.
Other way, is to use WITH statement, order table by value desc, use
rank() OVER (PARTITION BY ID) AS max_id
function and maximum value will be on max_id = 1, and then use
WHERE max_id = 1
to remove other rows.
But I think there is a way to do this better and I can't find one.
UPDATE:
A tricky solution to this problem is
SELECT *
FROM t t1
LEFT JOIN t t2 ON t1.value<t2.value
WHERE t2.value IS NULL
The simplest way is to sort the data and pull one row:
select t.*
from t
order by value desc
fetch first 1 row only;
If you want ties, you can add with ties to the fetch first.
Another method is:
select t.*
from t
where t.value = (select max(t2.value) from t t2);
This can have very good performance with an index on value.
Related
I want to find the max value in a column
ID CName Tot_Val PName
--------------------------------
1 1 100 P1
2 1 10 P2
3 2 50 P2
4 2 80 P1
Above is my table structure. I just want to find the max total value only from the table. In that four row ID 1 and 2 have same value in CName but total val and PName has different values. What I am expecting is have to find the max value in ID 1 and 2
Expected result:
ID CName Tot_Val PName
--------------------------------
1 1 100 P1
4 2 80 P1
I need result same as like mention above
select Max(Tot_Val), CName
from table1
where PName in ('P1', 'P2')
group by CName
This is query I have tried but my problem is that I am not able to bring PName in this table. If I add PName in the select list means it will showing the rows doubled e.g. Result is 100 rows but when I add PName in selected list and group by list it showing 600 rows. That is the problem.
Can someone please help me to resolve this.
One possible option is to use a subquery. Give each row a number within each CName group ordered by Tot_Val. Then select the rows with a row number equal to one.
select x.*
from ( select mt.ID,
mt.CName,
mt.Tot_Val,
mt.PName,
row_number() over(partition by mt.CName order by mt.Tot_Val desc) as No
from MyTable mt ) x
where x.No = 1;
An alternative would be to use a common table expression (CTE) instead of a subquery to isolate the first result set.
with x as
(
select mt.ID,
mt.CName,
mt.Tot_Val,
mt.PName,
row_number() over(partition by mt.CName order by mt.Tot_Val desc) as No
from MyTable mt
)
select x.*
from x
where x.No = 1;
See both solutions in action in this fiddle.
You can search top-n-per-group for this kind of a query.
There are two common ways to do it. The most efficient method depends on your indexes and data distribution and whether you already have another table with the list of all CName values.
Using ROW_NUMBER
WITH
CTE
AS
(
SELECT
ID, CName, Tot_Val, PName,
ROW_NUMBER() OVER (PARTITION BY CName ORDER BY Tot_Val DESC) AS rn
FROM table1
)
SELECT
ID, CName, Tot_Val, PName
FROM CTE
WHERE rn=1
;
Using CROSS APPLY
WITH
CTE
AS
(
SELECT CName
FROM table1
GROUP BY CName
)
SELECT
A.ID
,A.CName
,A.Tot_Val
,A.PName
FROM
CTE
CROSS APPLY
(
SELECT TOP(1)
table1.ID
,table1.CName
,table1.Tot_Val
,table1.PName
FROM table1
WHERE
table1.CName = CTE.CName
ORDER BY
table1.Tot_Val DESC
) AS A
;
See a very detailed answer on dba.se Retrieving n rows per group
, or here Get top 1 row of each group
.
CROSS APPLY might be as fast as a correlated subquery, but this often has very good performance (and better than ROW_NUMBER():
select t.*
from t
where t.tot_val = (select max(t2.tot_val)
from t t2
where t2.cname = t.cname
);
Note: The performance depends on having an index on (cname, tot_val).
I have a sql table like:
Name | Value
------+------
Andy | 22
Ben | 22
Carl | 22
David | 21
Eddie | 20
Frank | 19
I need an sql query that will return the tuples containing the maximum value, and if there is a tie (as in the example above), the relevant tuples in the tie will all need to be returned. Note that the values are already in descending order, and if there is no tie, one tuple is returned.
I have tried TOP and MAX in conjunction with GROUP BYs, but none of these are working.
TOP returns an error for invalid syntax and my attempts with MAX are flat out wrong.
In the above example, the tuples with Andy, Ben and Carl should be returned.
You mention TOP which suggests SQL Server. If so, you can use TOP WITH TIES:
select top (1) with ties t.*
from t
order by value desc;
Alas, that won't work in Postgres. Just use a correlated subquery:
select t.*
from t
where t.value = (select max(t2.value) from t);
In Postgres, you can use window function rank():
select name, value
from (
select
t.*,
rank() over(order by value desc) rn
from mytable t
) t
where rn = 1
The subquery ranks records per descending value; records that have the same value get the same rank. Then, the outer query filters on the top record(s).
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).
id value
2 20
1 30
3 15
5 25
I have this table and want to get max value and id. When i use select id,max(value) i've got 2,30 but the right answer is 1,30. I really need to get your attention.
Thank you very much
select id, value from `table` order by value desc limit 1
You can try using subquery
select * from tablename
where value in (select max(value) from tablename)
SELECT *
FROM `tablename`
WHERE value=(SELECT
MAX(value) as value
FROM tablename)
You can check this query. Giving result according your requirement.
SELECT top 1 id,max(value) FROM table
GROUP BY id
ORDER BY max(value) desc
Use subquery
select *
from t
where value = (select max(value) from table)
From the #Thorsten comments i noted that 1st query will return all ties of max value.
Or you can use order by with limit if it is mysql
select *
from table
order by value desc
limit 1
And 2nd query will return only the single row of highest value
I have a table that looks something like this:
first | last
John | Smith
Bob | dfgdf
John | fggf
John | Smith
And I want to run a query that will return only rows that have a unique last name for each first name. So only Bob dfgdf should be returned. Currently, I'm grouping twice and checking if count = 1, but is there a faster way?
SELECT first FROM (
SELECT first, last FROM table1 GROUP BY first, last
)as t1 GROUP BY first HAVING COUNT(*) = 1
Try this version:
SELECT first
FROM table1
GROUP BY first
HAVING COUNT(*) = COUNT(DISTINCT last);
Demo
This just retains only first names whose record count is coincident with the count of distinct last names, which would imply that each first name maps to a distinct last name.
Edit:
If you want all columns from all matching rows, then you may try:
WITH cte AS (
SELECT first
FROM table1
GROUP BY first
HAVING COUNT(*) = COUNT(DISTINCT last)
)
SELECT t1.*
FROM table1 t1
INNER JOIN cte t2
ON t1.first = t2.first;
I would do this as:
SELECT first
FROM table1
GROUP BY first
HAVING MIN(last) = MAX(last);
Actually, this should make use of an index on table1(first, last).
If the above doesn't use the index, then I would expect the fastest way to be:
select distinct on (first) first
from table1 t1
where not exists (select 1 from table1 tt1 where tt1.first = t1.first and tt1.last <> t1.last)
order by first;
This can make use of an index on table1(first, last) for performance.