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.
Related
I have a table like this.
id
grade_1
grade_2
createdAt
1
1
1
20220304
2
1
1
20220301
3
4
2
20220228
I want to select the current row(in here, id=1) and a row where the grade's value is different with the row I selected.(in here, id=3)
Like This
id
grade_1
grade_2
createdAt
1
1
1
20220304
3
4
2
20220228
I tried to use subquery but it doesn't really worked for me. Is there any way to skip the duplicated value when selecting table?
You can just do it with group by and a max value to retieve the one you want
SELECT
grade_1,
grade_2,
Max(createdAt)
from
yourTable
Group by
grade_1,
grade_2
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 need to find the repeated rows from a table where the first three columns will make up the primary key. Then after finding out which one's are repeated, those repeated rows need to be removed from the query results as this example shows:
Given this table. The first 3 columns act as the primary key.
--------------1 2 3 4 5 6-------------------------------------------------------------------------------------------------------------------------------1 2 3 9 8 9-------------------------------------------------------------------------------------------------------------------------------1 4 3 9 8 9-------------------------------------------------------------------------------------------------------------------------------3 4 2 2 2 1-------------------------------------------------------------------------------------------------------------------------------2 3 4 1 1 3-------------------------------------------------------------------------------------------------------------------------------2 3 4 9 9 0--------
Since 1 2 3 is the composite primary key. The first 2 rows should be considered repeated and therefore eliminated from the results. Just as the two 2 3 4 rows.
The only rows in the result set should be:
1 4 3 9 8 9 and 3 4 2 2 2 1
Could you please help?
Thanks a lot in advance..
Your question doesn't fully make sense. A composite primary key would prevent duplicates in the table. So, these columns are not declared as a comosite primary key if the data contains duplicates.
If you just one one row for each group, you can use row_number() for this, something like this (the column names are obviously invalid):
select t.*
from (select t.*, row_number() over (partition by 1, 2, 3 order by 1) as seqnum
from table t
) t
where seqnum = 1;
If you want to delete extra rows, you can try:
delete from t
where rowid not in (select min(rowid) from table t group by 1, 2, 3);
EDIT:
If you want to remove cases where the rows are repeated, then you want count() instead of row_number():
select t.*
from (select t.*, count() over (partition by 1, 2, 3) as cnt
from table t
) t
where cnt > 1;
I have this table my_table_c with the below values
SELECT * FROM my_table_c
ID GROUP_ID GROUP_VALUE
1 2 1
3 3 2
3 4 1
5 4 1
5 2 1
2 2 2
2 3 2
2 4 1
I am looking for this output where I get only the ID which do not have group_id 2. Additionally, I don't want to get the ID where group_id 2 is absent but other group ids are present.
If group_id 2 is absent, that's my target id.
So with the values shown in table above, I just expect ID = 3 to be returned as other ids 1, 5 and 2 each have rows where group_id = 2.
Can anyone please help with a query to fetch this result.
You could get all the id's that have group_id = 2 and use NOT IN
select *
from my_table_c
where id not in (select id from my_table_c where group_id = 2)
Another way but using NOT EXISTS
select *
from my_table_c mtcA
where not exists (select *
from my_table_c mtcB
where mtcA.id = mtcB.id and mtcB.group_ID = 2)
It's my first question here so I hope I can explain it well enough,
I want to order my data by amount of occurrences in the table.
My table is like this:
id Daynr
1 2
1 4
2 4
2 5
2 6
3 1
4 2
4 5
And I want it to sort it like this:
id Daynr
3 1
1 2
1 4
4 2
4 5
2 4
2 5
2 6
Player #3 has one day in the table, and Player #1 has 2.
My table is named "dayid"
Both id and Daynr are foreign keys, together making it a primary key
I hope this explains my problem enough, Please ask for more information it's my first time here.
Thanks in advance
You can do this by counting the number of times that things occur for each id. Most databases support window functions, so you can do this as:
select id, daynr
from (select t.*, count(*) over (partition by id) as cnt
from table t
) t
order by cnt, id;
You can also express this as a join:
select t.id, t.daynr
from table as t inner join
(select id, count(*) as cnt
from table
group by id
) as tg
on t.id = tg.id
order by tg.cnt, id;
Note that both of these include the id in the order by. That way, if two ids have the same count, all rows for the id will appear together.