How to update sql records by comparing duplicate strings? - sql

Question

I have a table below:
id | echantillon_dta | Est_en_double
1 | Bonjour | null
2 | Bonjour | null
3 | Bonjour | null
4 | Joke | null
5 | Joke | null
6 | | null
And after process query will show below:
id | echantillon_dta | Est_en_double
1 | Bonjour | 1
2 | Bonjour | 1
3 | Bonjour | 1
4 | Joke | 4
5 | Joke | 4
6 | | null
How to compare string vesus string? And how to update column like so?

Answer 1

you can use update by min(id) when Record_Details is same.
and there is a misdescription :
6 | Nope | 6 //No duplicates found, stay null
id 6 is no duplicate but isDuplicate column value is 6,shouldn't it be null?
so i use having count(1) > 1 to slove it.
CREATE TABLE Table1
("id" int, "Record_Details" varchar2(11), "isDuplicate" varchar2(4))
;
INSERT ALL
INTO Table1 ("id", "Record_Details", "isDuplicate")
VALUES (1, 'Hello World', NULL)
INTO Table1 ("id", "Record_Details", "isDuplicate")
VALUES (2, 'Hello World', NULL)
INTO Table1 ("id", "Record_Details", "isDuplicate")
VALUES (3, 'Hello World', NULL)
INTO Table1 ("id", "Record_Details", "isDuplicate")
VALUES (4, 'Joke', NULL)
INTO Table1 ("id", "Record_Details", "isDuplicate")
VALUES (5, 'Joke', NULL)
INTO Table1 ("id", "Record_Details", "isDuplicate")
VALUES (6, 'Nope', NULL)
SELECT * FROM dual
;
update (
select T.*
, (select min("id")
from Table1 Tmp
where Tmp."Record_Details" = T."Record_Details"
group by Tmp."Record_Details" having count(1) > 1 --No duplicates found, stay null
) as "new_isDuplicate"
from Table1 T
)
set "isDuplicate" = "new_isDuplicate"
6 rows affected
select * from Table1
id | Record_Details | isDuplicate
-: | :------------- | :----------
1 | Hello World | 1
2 | Hello World | 1
3 | Hello World | 1
4 | Joke | 4
5 | Joke | 4
6 | Nope | null
db<>fiddle here

Answer 2

You seem to want the minimum id with the same record_details.
This should work:
select t.*,
min(id) over (partition by record_details) as isDuplicate
from t;
If you want this as an update, a correlated subquery is a simple approach:
update t
set isduplicate = (select min(t2.id)
from t t2
where t2.record_details = t.record_details
);

Answer 3

You can use a MERGE statement and analytic function to find the duplicates:
Oracle Setup:
CREATE TABLE Table_name ( id, Record_Details, isDuplicate ) AS
SELECT 1, 'Hello World', CAST( NULL AS NUMBER ) FROM DUAL UNION ALL
SELECT 2, 'Hello World', NULL FROM DUAL UNION ALL
SELECT 3, 'Hello World', NULL FROM DUAL UNION ALL
SELECT 4, 'Joke', NULL FROM DUAL UNION ALL
SELECT 5, 'Joke', NULL FROM DUAL UNION ALL
SELECT 6, 'Nope', NULL FROM DUAL;
Merge:
MERGE INTO table_name dst
USING (
SELECT ROWID rid,
MIN( id ) OVER ( PARTITION BY Record_details ) AS dupe_id
FROM table_name
) src
ON (
dst.ROWID = src.RID
AND dst.id <> src.dupe_id -- remove this line if you want to update all rows
)
WHEN MATCHED THEN
UPDATE SET isDuplicate = dupe_id;
Output:
ID | RECORD_DETAILS | ISDUPLICATE
-: | :------------- | ----------:
1 | Hello World | null
2 | Hello World | 1
3 | Hello World | 1
4 | Joke | null
5 | Joke | 4
6 | Nope | null
db<>fiddle here