Remove duplicates with least row ids from Oracle - sql

Question

I have a database table which looks like
ID
Book_no
Book_name
Book_category
ID1
1
B1
CB1
ID1
2
B1
CB1
ID1
3
B2
CB1
ID1
4
B2
CB1
ID1
5
B3
CB1
ID2
1
B1
CB2
ID2
2
B1
CB2
ID2
3
B2
CB2
And the expected result is like
ID
Book_No
Book_name
Book_category
ID1
2
B1
CB1
ID1
4
B2
CB1
ID1
5
B3
CB1
ID2
2
B1
CB2
ID2
3
B2
CB2
I want to delete duplicate records from table on the basis of ID, Book_name and Book_category. Below query deletes the duplicate records, but the result is not expected one. As I want to delete all the duplicate records except the highest Book_no. Want to maintain the highest Book_no and delete all other duplicates.

Answer 1

You can DELETE correlating on the ROWID pseudo-column:
DELETE FROM table_name
WHERE ROWID IN (
SELECT rid
FROM (
SELECT ROWID AS rid,
ROW_NUMBER() OVER (
PARTITION BY id, book_name, book_category
ORDER BY book_no DESC
) AS rn
FROM table_name
)
WHERE rn > 1
);
Which, for the sample data:
CREATE TABLE table_name (id, book_no, book_name, book_category) AS
SELECT 'ID1', 1, 'B1', 'CB1' FROM DUAL UNION ALL
SELECT 'ID1', 2, 'B1', 'CB1' FROM DUAL UNION ALL
SELECT 'ID1', 3, 'B2', 'CB1' FROM DUAL UNION ALL
SELECT 'ID1', 4, 'B2', 'CB1' FROM DUAL UNION ALL
SELECT 'ID1', 5, 'B3', 'CB1' FROM DUAL UNION ALL
SELECT 'ID2', 1, 'B1', 'CB2' FROM DUAL UNION ALL
SELECT 'ID2', 2, 'B1', 'CB2' FROM DUAL UNION ALL
SELECT 'ID2', 3, 'B2', 'CB2' FROM DUAL;
Then the remaining rows are:
SELECT * FROM table_name;
ID
BOOK_NO
BOOK_NAME
BOOK_CATEGORY
ID1
2
B1
CB1
ID1
4
B2
CB1
ID1
5
B3
CB1
ID2
2
B1
CB2
ID2
3
B2
CB2
sqlfiddle here

Answer 2

You can use lead() and filter where the name changes:
select t.*
from (select t.*,
lead(book_name) over (partition by id, book_category order by book_no) as next_book_name
from t
) t
where next_book_name is null or next_book_name <> book_name;

Answer 3

Assuming your table looks like this:
create table books (id, book_no, book_name, book_category) as
select 'ID1', 1, 'B1', 'CB1' from dual union all
select 'ID1', 2, 'B1', 'CB1' from dual union all
select 'ID1', 3, 'B2', 'CB1' from dual union all
select 'ID1', 4, 'B2', 'CB1' from dual union all
select 'ID1', 5, 'B3', 'CB1' from dual union all
select 'ID2', 1, 'B1', 'CB2' from dual union all
select 'ID2', 2, 'B1', 'CB2' from dual union all
select 'ID2', 3, 'B2', 'CB2' from dual
;
You can use a delete statement in which you compare each row to the ones you want to keep. The ones you want to keep have max(book_no) when grouped by the other columns. So:
delete from books
where (id, book_no, book_name, book_category) not in
(
select id, max(book_no), book_name, book_category
from books
group by id, book_name, book_category
)
;
This assumes that the columns are non-null; if you may have null in the table, you will need to rewrite this a little more carefully, with a not exists condition instead of not in, but the idea is the same.

Answer 4

You can use first_value for finding the required id and can remove others using delete.
SELECT DISTINCT a.*, FIRST_VALUE(a.book_name)
OVER (ORDER BY a.book_name DESC
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
AS "HIGHEST"
FROM ( select * from books group by id, Book_name, book_category ) a;
SELECT DISTINCT FIRST_VALUE(column_name)
OVER (ORDER BY column_name DESC
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
AS "HIGHEST"
FROM (select * from tables group by "column_names_to_be_grouped");