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Selecting distinct records
Posted on 2010-08-28
I am writing a select query from a table TEST having three colums A,B,C in which i want to select distinct records on the basis of both the colums A and B.
If i give:
select distinct A,B,C from test;
it gives only the distinct records on the basis of column A. I tried this also:
select distinct A,B,C from test group by A,B;
but not working. Kindly suggest.
If i give:
select distinct A,B,C from test;
it gives only the distinct records on the basis of column A. I tried this also:
select distinct A,B,C from test group by A,B;
but not working. Kindly suggest.
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7 Comments
Active 4 days ago
Try using:
select A,B,MAX(C) as C
from test
group by A,B;
or
select A,B,MAX(C) as C
from test
group by A,B;
select A,B,MAX(C) as C
from test
group by A,B;
or
select A,B,MAX(C) as C
from test
group by A,B;
I dont understand why did u suggest using max(C), i think that will select max value for column C but my problem is different.
I want to select distinct records on the basis of both column A and B but not column C.
I want to select distinct records on the basis of both column A and B but not column C.
Active 4 days ago
Then try this:
SELECT A, B, C
FROM (
select A,B,C, ROW_NUMBER() OVER ( Partition By A, B order by C) as rnum
from test ) temp
WHERE rnum = 1
SELECT A, B, C
FROM (
select A,B,C, ROW_NUMBER() OVER ( Partition By A, B order by C) as rnum
from test ) temp
WHERE rnum = 1
Active 2 days ago
Hi mohitgyl,
Can you explain a bit about what you see in the original query?
SELECT distinct a, b, c FROM mytable;
That query will filter out all rows where a,b,c are ALL exactly like the values of another row. (It will be selected only once.) I does not filter only on column "a".
Kent
Can you explain a bit about what you see in the original query?
SELECT distinct a, b, c FROM mytable;
That query will filter out all rows where a,b,c are ALL exactly like the values of another row. (It will be selected only once.) I does not filter only on column "a".
Kent
Active 1 day ago
...it gives only the distinct records on the basis of column A.
I am not clear at all what the problem is. It sounds as if you are trying to get DISTINCT A, DISTINCT B and DISTINCT C, all somehow included in a single result set.
But that doesn't make sense to me.
Can you supply a few example rows from a table and show what result you expect to see from those rows?
Tom
I am not clear at all what the problem is. It sounds as if you are trying to get DISTINCT A, DISTINCT B and DISTINCT C, all somehow included in a single result set.
But that doesn't make sense to me.
Can you supply a few example rows from a table and show what result you expect to see from those rows?
Tom
Active 1 day ago
I mistakenly included "DISTINCT C" in my previous comment. But it's still not clear about the meaning two DISTINCT columns while a third column is not DISTINCT.
...distinct records on the basis of both column A and B but not column C.
You also said "why did u suggest using max(C)". If you don't use max(C) or some similar function, how else while the query know which C value to retrieve?
A B C
-- -- ---
a1 b1 c1
a1 b1 c2
a2 b2 c3
a2 b2 c4
a3 b4 c5
a3 b5 c6
a4 b4 c7
DISTINCT values for A are (a1, a2, a3, a4). DISTINCT values for B are (b1, b2, b4, b5).
So, DISTINCT A CONCAT B values are (a1b1, a2b2, a3b4, a3b5, a4b4).
For the (a2b2) value, which value for C should be in the result set -- c3 or c4? There can be only one because the (a2b2) value must be DISTINCT. You need some way to choose which value of C should be picked. The max(C) function will make the choice between (c3) and (c4)
Show a sample of data and show your expected result, please.
Tom
...distinct records on the basis of both column A and B but not column C.
You also said "why did u suggest using max(C)". If you don't use max(C) or some similar function, how else while the query know which C value to retrieve?
A B C
-- -- ---
a1 b1 c1
a1 b1 c2
a2 b2 c3
a2 b2 c4
a3 b4 c5
a3 b5 c6
a4 b4 c7
DISTINCT values for A are (a1, a2, a3, a4). DISTINCT values for B are (b1, b2, b4, b5).
So, DISTINCT A CONCAT B values are (a1b1, a2b2, a3b4, a3b5, a4b4).
For the (a2b2) value, which value for C should be in the result set -- c3 or c4? There can be only one because the (a2b2) value must be DISTINCT. You need some way to choose which value of C should be picked. The max(C) function will make the choice between (c3) and (c4)
Show a sample of data and show your expected result, please.
Tom
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