We have a process that creates a table of duplicate records based on some arbitrary rules (details not relevant).
Every record gets checked against all other records and if a suspected duplicate is found both it and the duplicate are stored in a dupes table to be manually reviewed.
This results in a table something like this:
dupId, originalId, duplicateId
1 1 2
2 1 3
3 1 4
4 2 3
5 2 4
6 3 4
7 5 6
8 5 7
9 6 7
10 8 9
You can see here record #1 has 3 other records it is similar to (#2,#3 and #4) and they are each similar to each other.
Record #5 has 2 duplicates (#6 and #7) and record #8 has only 1 (#9).
I want to query the duplicates into sets, so my results would look something like this:
setId recordId
1 1
1 2
1 3
1 4
2 5
2 6
2 7
3 8
3 9
But I am too old/slow/tired/rubbish and a bit out of my depth here.
Currently, when checking for duplicates if the record pairing is already in the table we don't insert it twice (i.e. you don't see both sides of the duplicate pairing) but can easily do so if it makes the querying simpler.
Any advice much appreciated!
Duplicates seems to be transitive, so you have all pairs. That is, the "original" id has the information you need.
But it is not included in the duplicates and you want that. So:
select dense_rank() over (order by originalid) as setid, duplicateid
from ((select originalid, duplicateid
from t
where not exists (select 1 from t t2 where t.originalid = t2.duplicateid)
) union all
(select distinct originalid, originalid
from t
where not exists (select 1 from t t2 where t.originalid = t2.duplicateid)
)
) i
order by setid;
I am trying to update a column in a table so that the Index column (which is currently arbitrary numbers) is renumbered sequentially starting at 1000 with increments of 10, and this sequence restarts every time the Group changes.
I have tried ROWNUMBER() with PARTITION and trying to define a SEQUENCE, but I can't seem to get the result I'm looking for.
Table 1
ID Group Index
1 A 1
2 A 2
3 B 3
4 B 4
5 B 5
6 C 6
7 D 7
What I want:
Table 1
ID Group Index
1 A 1000
2 A 1010
3 B 1000
4 B 1010
5 B 1020
6 C 1000
7 D 1000
You can use row_number() with some arithmetic:
select t.*,
990 + 10 * row_number() over (partition by group order by id) as index
from t;
Note that group and index are SQL reserved words, so they are really bad column names.
I have table like this-
id object_id product_id
1 1 1
2 1 1
4 2 2
6 3 2
7 3 2
8 1 2
9 1 1
I want to delete all rows except these-
1 1 1
4 2 2
6 3 2
9 1 2
Basically there are duplicates and I want to remove them but keep one copy intact.
what would be the most efficient way for this?
If this is a one-off then you can simply identify the records you want to keep like so:
SELECT MIN(id) AS id
FROM yourtable
GROUP BY object_id, product_id;
You want to check that this works before you do the next thing and actually throw records out. To actually delete those duplicate records you do:
DELETE FROM yourtable WHERE id NOT IN (
SELECT MIN(id) AS id
FROM yourtable
GROUP BY object_id, product_id
);
The MIN(id) obviously always returns the record with the lowest id for a set of (object_id, product_id). Change as desired.
So I have a table of aliases linked to record ids. I need to find duplicate aliases with unique record ids. To explain better:
ID Alias Record ID
1 000123 4
2 000123 4
3 000234 4
4 000123 6
5 000345 6
6 000345 7
The result of a query on this table should be something to the effect of
000123 4 6
000345 6 7
Indicating that both record 4 and 6 have an alias of 000123 and both record 6 and 7 have an alias of 000345.
I was looking into using GROUP BY but if I group by alias then I can't select record id and if I group by both alias and record id it will only return the first two rows in this example where both columns are duplicates. The only solution I've found, and it's a terrible one that crashed my server, is to do two different selects for all the data and then join them
ON [T_1].[ALIAS] = [T_2].[ALIAS] AND NOT [T_1].[RECORD_ID] = [T_2].[RECORD_ID]
Are there any solutions out there that would work better? As in, not crash my server when run on a few hundred thousand records?
It looks as if you have two requirements:
Identify all aliases that have more than one record id, and
List the record ids for these aliases horizontally.
The first is a lot easier to do than the second. Here's some SQL that ought to get you where you want with the first:
WITH A -- Get a list of unique combinations of Alias and [Record ID]
AS (
SELECT Distinct
Alias
, [Record ID]
FROM T1
)
, B -- Get a list of all those Alias values that have more than one [Record ID] associated
AS (
SELECT Alias
FROM A
GROUP BY
Alias
HAVING COUNT(*) > 1
)
SELECT A.Alias
, A.[Record ID]
FROM A
JOIN B
ON A.Alias = B.Alias
Now, as for the second. If you're satisfied with the data in this form:
Alias Record ID
000123 4
000123 6
000345 6
000345 7
... you can stop there. Otherwise, things get tricky.
The PIVOT command will not necessarily help you, because it's trying to solve a different problem than the one you have.
I am assuming that you can't necessarily predict how many duplicate Record ID values you have per Alias, and thus don't know how many columns you'll need.
If you have only two, then displaying each of them in a column becomes a relatively trivial exercise. If you have more, I'd urge you to consider whether the destination for these records (a report? A web page? Excel?) might be able to do a better job of displaying them horizontally than SQL Server can do in returning them arranged horizontally.
Perhaps what you want is just the min() and max() of RecordId:
select Alias, min(RecordID), max(RecordId)
from yourTable t
group by Alias
having min(RecordId) <> max(RecordId)
You can also count the number of distinct values, using count(distinct):
select Alias, count(distinct RecordId) as NumRecordIds, min(RecordID), max(RecordId)
from yourTable t
group by Alias
having count(DISTINCT RecordID) > 1;
This will give all repeated values:
select Alias, count(RecordId) as NumRecordIds,
from yourTable t
group by Alias
having count(RecordId) <> count(distinct RecordId);
I agree with Ann L's answer but would like to show how you can use window functions with CTE's as you may prefer the readability.
(Re: how to pivot horizontally, I again agree with Ann)
create temporary table things (
id serial primary key,
alias varchar,
record_id int
)
insert into things (alias, record_id) values
('000123', 4),
('000123', 4),
('000234', 4),
('000123', 6),
('000345', 6),
('000345', 7);
with
things_with_distinct_aliases_and_record_ids as (
select distinct on (alias, record_id)
id,
alias,
record_id
from things
),
things_with_unique_record_id_counts_per_alias as (
select *,
COUNT(*) OVER(PARTITION BY alias) as unique_record_ids_count
from things_with_distinct_aliases_and_record_ids
)
select * from things_with_unique_record_id_counts_per_alias
where unique_record_ids_count > 1
The first CTE gets all the unique alias/record id combinations. E.g.
id | alias | record_id
----+--------+-----------
1 | 000123 | 4
4 | 000123 | 6
3 | 000234 | 4
5 | 000345 | 6
6 | 000345 | 7
The second CTE simply creates a new column for the above and adds the count of record ids for each alias. This allows you to filter only those aliases which have more than one record id associated with them.
id | alias | record_id | unique_record_ids_count
----+--------+-----------+-------------------------
1 | 000123 | 4 | 2
4 | 000123 | 6 | 2
3 | 000234 | 4 | 1
5 | 000345 | 6 | 2
6 | 000345 | 7 | 2
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By using SQlite, I'd like to get all rows that show in a specific column only one single distinct value. Like from following table:
A B
1 2
2 1
3 2
4 3
5 1
6 1
7 2
8 4
9 2
Here I'd like to get only row Nr. 4 an 8 as there values (3 and 4) occur only once in the entire column.
You could use a query like this:
SELECT *
FROM mytable
WHERE B IN (SELECT B FROM mytable GROUP BY B HAVING COUNT(DISTINCT A)=1)
Please see fiddle here.
Subquery will return all B values that are present only once (you could also use HAVING COUNT(*)=1 in this case), the outer query will return all rows where B is returned by the subquery.