I am using postgres.
I want to delete Duplicate rows.
The condition is that , 1 copy from the set of duplicate rows would not be deleted.
i.e : if there are 5 duplicate records then 4 of them will be deleted.
Try the steps described in this article: Removing duplicates from a PostgreSQL database.
It describes a situation when you have to deal with huge amount of data which isn't possible to group by.
A simple solution would be this:
DELETE FROM foo
WHERE id NOT IN (SELECT min(id) --or max(id)
FROM foo
GROUP BY hash)
Where hash is something that gets duplicated.
delete from table
where not id in
(select max(id) from table group by [duplicate row])
This is random (max Value) choice which row you need to keep.
If you have aggre whit this please provide more details
The fastest is is join to the same table.
http://www.postgresql.org/docs/8.1/interactive/sql-delete.html
CREATE TABLE test(id INT,id2 INT);
CREATE TABLE
mapy=# INSERT INTO test VALUES(1,2);
INSERT 0 1
mapy=# INSERT INTO test VALUES(1,3);
INSERT 0 1
mapy=# INSERT INTO test VALUES(1,4);
INSERT 0 1
DELETE FROM test t1 USING test t2 WHERE t1.id=t2.id AND t1.id2<t2.id2;
DELETE 2
mapy=# SELECT * FROM test;
id | id2
----+-----
1 | 4
(1 row)
delete from table t1
where rowid > (SELECT min(rowid) FROM table t2 group by
t2.id,t2.name );
DELETE f1 from foo as f1, foo as f2
where f1.duplicate_column= f2.duplicate_column
AND f1.id > f2.id;
Related
I have a table that looks like:
ID|CREATED |VALUE
1 |1649122158|200
1 |1649122158|200
1 |1649122158|200
That I'd like to look like:
ID|CREATED |VALUE
1 |1649122158|200
And I run the following query:
DELETE FROM MY_TABLE T USING (SELECT ID,CREATED,ROW_NUMBER() OVER (PARTITION BY ID ORDER BY CREATED DESC) AS RANK_IN_KEY FROM MY_TABLE T) X WHERE X.RANK_IN_KEY <> 1 AND T.ID = X.ID AND T.CREATED = X.CREATED
But it removes everything from MY_TABLE and not just other rows with the same value. This is more than just selecting distinct records, I'd like to enforce a unique constraint to get the latest value of ID and keep just one record for it, even if there were duplicates.
So
ID|CREATED |VALUE
1 |1649122158|200
1 |1649122159|300
2 |1649122158|200
2 |1649122158|200
3 |1649122170|500
3 |1649122160|200
Would become (using the same final unique constraint statement):
ID|CREATED |VALUE
1 |1649122159|300
2 |1649122158|200
3 |1649122170|500
How can I improve my logic to properly handle these unique constraint modifications?
Check out this post: https://community.snowflake.com/s/question/0D50Z00008EJgemSAD/how-to-delete-duplicate-records-
If all columns make up a unique records, the recommended solution is the insert all the records into a new table with SELECT DISTINCT * and do a swap. You could also do a INSERT OVERWRITE INTO the same table.
Something like INSERT OVERWRITE INTO tableA SELECT DISTINCT * FROM tableA;
The following setup should leave rows with id of 1 and 3. And not delete all rows as you say.
Schema
create table t (
id int,
created int ,
value int
);
insert into t values(1, 1649122158, 200);
insert into t values(1 ,1649122159, 300);
insert into t values(2 ,1649122158, 200);
insert into t values(2 ,1649122158, 200);
insert into t values(3 ,1649122170, 500);
insert into t values(3 ,1649122160, 200);
Delete statement
with x as (
SELECT
id, created,
row_number() over(partition by id) as r
FROM t
)
delete from t
using x
where x.id = t.id and x.r <> 1 and x.created = t.created
;
Output
select * from t;
1 1649122158 200
3 1649122170 500
The logic is such, that the table in the using clause is joined with the operated on table. Following the join logic, it just matches by some key. In your case, you have key as {id,created}. This key is duplicated for rows with id of 2. So the whole group is deleted.
I'm no savvy in database schemas. But as a thought, you may add a row with a rank to existing table. And after that you can proceed with deletion. This way you do not need to create other table and insert values to that. Be warned that data may become fragmented(physically, on disks). So you will need to run some kind of tune up later.
Update
You may find this almost one-liner interesting:
SO answer
I will duplicate code here, as it is so small and well written.
WITH
u AS (SELECT DISTINCT * FROM your_table),
x AS (DELETE FROM your_table)
INSERT INTO your_table SELECT * FROM u;
I am trying to make a query to remove the record in table 1 based on the duplicate records found in table 2. id is the common link between these two tables. The Database is oracle. I am new in writing up queries and the below is the query i came up with so far which is not working out. Can anyone please suggest?
I am actually trying to delete record based on the id in table 1 on a condition when there are duplicate records in table 2 for that id as well as one more column? Below is the error message i am getting, am really not sure if query is accurate either or need to re write the whole query itself?
"invalid sql statement" - ORA-00900
DELETE TABLE AS m WHERE m.id IN
(SELECT id from table2 t WHERE ROWID >
(SELECT MIN(ROWID) FROM table2 r WHERE t.column2 = r.column2);
You can try the following one(use only tab as the table in the statement) :
create table tab ( id int, val int );
insert into tab values(1 ,331);
insert into tab values(1 ,332);
insert into tab values(2 ,333);
insert into tab values(2 ,333);
select * from tab;
ID VAL
1 331
1 332
2 333
2 333
delete tab a
where
rowid >
(select min(rowid)
from tab b
where b.id=a.id
group by b.id);
select * from tab;
ID VAL
1 331
2 333
sqlfiddle demo
As a side note : table is a reserved keyword in Oracle and may not be a table name, "table" may be used alternatively.
You would find the duplicates somehow. This is a little unclear, but perhaps:
select t2.column2, count(*)
from table2 t2
group by t2.column2
having count(*) >= 2;
You can then put this into the delete:
delete from m
where m.id in (select t2.column2
from table2 t2
group by t2.column2
having count(*) >= 2
);
I think this requirement is rarely encountered so I couldn't search for similar questions.
I have a table that needs to update the ID. For example ID 123 in table1 is actually supposed to be 456. I have a separate reference table built that stores the mapping (e.g. old 123 maps to new id 456).
I used the below query but apparently it returned error 38104, columns referenced in the ON clause cannot be updated.
MERGE INTO table1
USING ref_table ON (table1.ID = ref_table.ID_Old)
WHEN MATCHED THEN UPDATE SET table.ID = ref_table.ID_New;
Is there other way to achieve my purpose?
Thanks and much appreciated for your answer!
Use the ROWID pseudocolumn:
SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE TABLE1( ID ) AS
SELECT 1 FROM DUAL UNION ALL
SELECT 2 FROM DUAL UNION ALL
SELECT 3 FROM DUAL;
CREATE TABLE REF_TABLE( ID_OLD, ID_NEW ) AS
SELECT 1, 4 FROM DUAL UNION ALL
SELECT 2, 5 FROM DUAL;
MERGE INTO TABLE1 dst
USING ( SELECT t.ROWID AS rid,
r.id_new
FROM TABLE1 t
INNER JOIN REF_TABLE r
ON ( t.id = r.id_old ) ) src
ON ( dst.ROWID = src.RID )
WHEN MATCHED THEN
UPDATE SET id = src.id_new;
Query 1:
SELECT * FROM table1
Results:
| ID |
|----|
| 4 |
| 5 |
| 3 |
You can't update a column used in the ON clause in a MERGE. But if you don't need to make other changes that MERGE allows like WHEN NOT MATCHED or deleting, etc. you can just use a UPDATE to achieve this.
You mentioned this is an ID that needs an update. Here's an example using a scalar subquery. As it is an ID, this presumes UNIQUE ID_OLD values in REF_TABLE. I wasn't sure if Every row needs an update or only a sub-set, so set the update here to only update rows that have a value in REF_TABLE.
CREATE TABLE TABLE1(
ID NUMBER
);
CREATE TABLE REF_TABLE(
ID_OLD NUMBER,
ID_NEW NUMBER
);
INSERT INTO TABLE1 VALUES (1);
INSERT INTO TABLE1 VALUES (2);
INSERT INTO TABLE1 VALUES (100);
INSERT INTO REF_TABLE VALUES (1,10);
INSERT INTO REF_TABLE VALUES (2,20);
Initial State:
SELECT * FROM TABLE1;
ID
1
2
100
Then make the UPDATE
UPDATE TABLE1
SET TABLE1.ID = (SELECT REF_TABLE.ID_NEW
FROM REF_TABLE
WHERE REF_TABLE.ID_OLD = ID)
WHERE TABLE1.ID IN (SELECT REF_TABLE.ID_OLD
FROM REF_TABLE);
2 rows updated.
And check the change:
SELECT * FROM TABLE1;
ID
10
20
100
I have an Access table of the form (I'm simplifying it a bit)
ID AutoNumber Primary Key
SchemeName Text (50)
SchemeNumber Text (15)
This contains some data eg...
ID SchemeName SchemeNumber
--------------------------------------------------------------------
714 Malcolm ABC123
80 Malcolm ABC123
96 Malcolms Scheme ABC123
101 Malcolms Scheme ABC123
98 Malcolms Scheme DEF888
654 Another Scheme BAR876
543 Whatever Scheme KJL111
etc...
Now. I want to remove duplicate names under the same SchemeNumber. But I want to leave the record which has the longest SchemeName for that scheme number. If there are duplicate records with the same longest length then I just want to leave only one, say, the lowest ID (but any one will do really). From the above example I would want to delete IDs 714, 80 and 101 (to leave only 96).
I thought this would be relatively easy to achieve but it's turning into a bit of a nightmare! Thanks for any suggestions. I know I could loop it programatically but I'd rather have a single DELETE query.
See if this query returns the rows you want to keep:
SELECT r.SchemeNumber, r.SchemeName, Min(r.ID) AS MinOfID
FROM
(SELECT
SchemeNumber,
SchemeName,
Len(SchemeName) AS name_length,
ID
FROM tblSchemes
) AS r
INNER JOIN
(SELECT
SchemeNumber,
Max(Len(SchemeName)) AS name_length
FROM tblSchemes
GROUP BY SchemeNumber
) AS w
ON
(r.SchemeNumber = w.SchemeNumber)
AND (r.name_length = w.name_length)
GROUP BY r.SchemeNumber, r.SchemeName
ORDER BY r.SchemeName;
If so, save it as qrySchemes2Keep. Then create a DELETE query to discard rows from tblSchemes whose ID value is not found in qrySchemes2Keep.
DELETE
FROM tblSchemes AS s
WHERE Not Exists (SELECT * FROM qrySchemes2Keep WHERE MinOfID = s.ID);
Just beware, if you later use Access' query designer to make changes to that DELETE query, it may "helpfully" convert the SQL to something like this:
DELETE s.*, Exists (SELECT * FROM qrySchemes2Keep WHERE MinOfID = s.ID)
FROM tblSchemes AS s
WHERE (((Exists (SELECT * FROM qrySchemes2Keep WHERE MinOfID = s.ID))=False));
DELETE FROM Table t1
WHERE EXISTS (SELECT 1 from Table t2
WHERE t1.SchemeNumber = t2.SchemeNumber
AND Length(t2.SchemeName) > Length(t1.SchemeName)
)
Depend on your RDBMS you may use function different from Length (Oracle - length, mysql - length, sql server - LEN)
delete ShortScheme
from Scheme ShortScheme
join Scheme LongScheme
on ShortScheme.SchemeNumber = LongScheme.SchemeNumber
and (len(ShortScheme.SchemeName) < len(LongScheme.SchemeName) or (len(ShortScheme.SchemeName) = len(LongScheme.SchemeName) and ShortScheme.ID > LongScheme.ID))
(SQL Server flavored)
Now updated to include the specified tie resolution. Although, you may get better performance doing it in two queries: first deleting the schemes with shorter names as in my original query and then going back and deleting the higher ID where there was a tie in name length.
I'd do this in multiple steps. Large delete operations done in a single step make me too nervous -- what if you make a mistake? There's no sql 'undo' statement.
-- Setup the data
DROP Table foo;
DROP Table bar;
DROP Table bat;
DROP Table baz;
CREATE TABLE foo (
id int(11) NOT NULL,
SchemeName varchar(50),
SchemeNumber varchar(15),
PRIMARY KEY (id)
);
insert into foo values (714, 'Malcolm', 'ABC123' );
insert into foo values (80, 'Malcolm', 'ABC123' );
insert into foo values (96, 'Malcolms Scheme', 'ABC123' );
insert into foo values (101, 'Malcolms Scheme', 'ABC123' );
insert into foo values (98, 'Malcolms Scheme', 'DEF888' );
insert into foo values (654, 'Another Scheme ', 'BAR876' );
insert into foo values (543, 'Whatever Scheme ', 'KJL111' );
-- Find all the records that have dups, find the longest one
create table bar as
select max(length(SchemeName)) as max_length, SchemeNumber
from foo
group by SchemeNumber
having count(*) > 1;
-- Find the one we want to keep
create table bat as
select min(a.id) as id, a.SchemeNumber
from foo a join bar b on a.SchemeNumber = b.SchemeNumber
and length(a.SchemeName) = b.max_length
group by SchemeNumber;
-- Select into this table all the rows to delete
create table baz as
select a.id from foo a join bat b where a.SchemeNumber = b.SchemeNumber
and a.id != b.id;
This will give you a new table with only records for rows that you want to remove.
Now check these out and make sure that they contain only the rows you want deleted. This way you can make sure that when you do the delete, you know exactly what to expect. It should also be pretty fast.
Then when you're ready, use this command to delete the rows using this command.
delete from foo where id in (select id from baz);
This seems like more work because of the different tables, but it's safer probably just as fast as the other ways. Plus you can stop at any step and make sure the data is what you want before you do any actual deletes.
If your platform supports ranking functions and common table expressions:
with cte as (
select row_number()
over (partition by SchemeNumber order by len(SchemeName) desc) as rn
from Table)
delete from cte where rn > 1;
try this:
Select * From Table t
Where Len(SchemeName) <
(Select Max(Len(Schemename))
From Table
Where SchemeNumber = t.SchemeNumber )
And Id >
(Select Min (Id)
From Table
Where SchemeNumber = t.SchemeNumber
And SchemeName = t.SchemeName)
or this:,...
Select * From Table t
Where Id >
(Select Min(Id) From Table
Where SchemeNumber = t.SchemeNumber
And Len(SchemeName) <
(Select Max(Len(Schemename))
From Table
Where SchemeNumber = t.SchemeNumber))
if either of these selects the records that should be deleted, just change it to a delete
Delete
From Table t
Where Len(SchemeName) <
(Select Max(Len(Schemename))
From Table
Where SchemeNumber = t.SchemeNumber )
And Id >
(Select Min (Id)
From Table
Where SchemeNumber = t.SchemeNumber
And SchemeName = t.SchemeName)
or using the second construction:
Delete From Table t Where Id >
(Select Min(Id) From Table
Where SchemeNumber = t.SchemeNumber
And Len(SchemeName) <
(Select Max(Len(Schemename))
From Table
Where SchemeNumber = t.SchemeNumber))
I was wondering if it is possible to move all rows of data from one table to another, that match a certain query?
For example, I need to move all table rows from Table1 to Table2 where their username = 'X' and password = 'X', so that they will no longer appear in Table1.
I'm using SQL Server 2008 Management Studio.
Should be possible using two statements within one transaction, an insert and a delete:
BEGIN TRANSACTION;
INSERT INTO Table2 (<columns>)
SELECT <columns>
FROM Table1
WHERE <condition>;
DELETE FROM Table1
WHERE <condition>;
COMMIT;
This is the simplest form. If you have to worry about new matching records being inserted into table1 between the two statements, you can add an and exists <in table2>.
This is an ancient post, sorry, but I only came across it now and I wanted to give my solution to whoever might stumble upon this one day.
As some have mentioned, performing an INSERT and then a DELETE might lead to integrity issues, so perhaps a way to get around it, and to perform everything neatly in a single statement, is to take advantage of the [deleted] temporary table.
DELETE FROM [source]
OUTPUT [deleted].<column_list>
INTO [destination] (<column_list>)
All these answers run the same query for the INSERT and DELETE. As mentioned previously, this risks the DELETE picking up records inserted between statements and could be slow if the query is complex (although clever engines "should" make the second call fast).
The correct way (assuming the INSERT is into a fresh table) is to do the DELETE against table1 using the key field of table2.
The delete should be:
DELETE FROM tbl_OldTableName WHERE id in (SELECT id FROM tbl_NewTableName)
Excuse my syntax, I'm jumping between engines but you get the idea.
A cleaner representation of what some other answers have hinted at:
DELETE sourceTable
OUTPUT DELETED.*
INTO destTable (Comma, separated, list, of, columns)
WHERE <conditions (if any)>
Yes it is. First INSERT + SELECT and then DELETE orginals.
INSERT INTO Table2 (UserName,Password)
SELECT UserName,Password FROM Table1 WHERE UserName='X' AND Password='X'
then delete orginals
DELETE FROM Table1 WHERE UserName='X' AND Password='X'
you may want to preserve UserID or someother primary key, then you can use IDENTITY INSERT to preserve the key.
see more on SET IDENTITY_INSERT on MSDN
You should be able to with a subquery in the INSERT statement.
INSERT INTO table1(column1, column2) SELECT column1, column2 FROM table2 WHERE ...;
followed by deleting from table1.
Remember to run it as a single transaction so that if anything goes wrong you can roll the entire operation back.
Use this single sql statement which is safe no need of commit/rollback with multiple statements.
INSERT Table2 (
username,password
) SELECT username,password
FROM (
DELETE Table1
OUTPUT
DELETED.username,
DELETED.password
WHERE username = 'X' and password = 'X'
) AS RowsToMove ;
Works on SQL server make appropriate changes for MySql
Try this
INSERT INTO TABLE2 (Cols...) SELECT Cols... FROM TABLE1 WHERE Criteria
Then
DELETE FROM TABLE1 WHERE Criteria
You could try this:
SELECT * INTO tbl_NewTableName
FROM tbl_OldTableName
WHERE Condition1=#Condition1Value
Then run a simple delete:
DELETE FROM tbl_OldTableName
WHERE Condition1=#Condition1Value
You may use "Logical Partitioning" to switch data between tables:
By updating the Partition Column, data will be automatically moved to the other table:
here is the sample:
CREATE TABLE TBL_Part1
(id INT NOT NULL,
val VARCHAR(10) NULL,
PartitionColumn VARCHAR(10) CONSTRAINT CK_Part1 CHECK(PartitionColumn = 'TBL_Part1'),
CONSTRAINT TBL_Part1_PK PRIMARY KEY(PartitionColumn, id)
);
CREATE TABLE TBL_Part2
(id INT NOT NULL,
val VARCHAR(10) NULL,
PartitionColumn VARCHAR(10) CONSTRAINT CK_Part2 CHECK(PartitionColumn = 'TBL_Part2'),
CONSTRAINT TBL_Part2_PK PRIMARY KEY(PartitionColumn, id)
);
GO
CREATE VIEW TBL(id, val, PartitionColumn)
WITH SCHEMABINDING
AS
SELECT id, val, PartitionColumn FROM dbo.TBL_Part1
UNION ALL
SELECT id, val, PartitionColumn FROM dbo.TBL_Part2;
GO
--Insert sample to TBL ( will be inserted to Part1 )
INSERT INTO TBL
VALUES(1, 'rec1', 'TBL_Part1');
INSERT INTO TBL
VALUES(2, 'rec2', 'TBL_Part1');
GO
--Query sub table to verify
SELECT * FROM TBL_Part1
GO
--move the data to table TBL_Part2 by Logical Partition switching technique
UPDATE TBL
SET
PartitionColumn = 'TBL_Part2';
GO
--Query sub table to verify
SELECT * FROM TBL_Part2
Here is how do it with single statement
WITH deleted_rows AS (
DELETE FROM source_table WHERE id = 1
RETURNING *
)
INSERT INTO destination_table
SELECT * FROM deleted_rows;
EXAMPLE:
postgres=# select * from test1 ;
id | name
----+--------
1 | yogesh
2 | Raunak
3 | Varun
(3 rows)
postgres=# select * from test2;
id | name
----+------
(0 rows)
postgres=# WITH deleted_rows AS (
postgres(# DELETE FROM test1 WHERE id = 1
postgres(# RETURNING *
postgres(# )
postgres-# INSERT INTO test2
postgres-# SELECT * FROM deleted_rows;
INSERT 0 1
postgres=# select * from test2;
id | name
----+--------
1 | yogesh
(1 row)
postgres=# select * from test1;
id | name
----+--------
2 | Raunak
3 | Varun
If the two tables use the same ID or have a common UNIQUE key:
1) Insert the selected record in table 2
INSERT INTO table2 SELECT * FROM table1 WHERE (conditions)
2) delete the selected record from table1 if presents in table2
DELETE FROM table1 as A, table2 as B WHERE (A.conditions) AND (A.ID = B.ID)
It will create a table and copy all the data from old table to new table
SELECT * INTO event_log_temp FROM event_log
And you can clear the old table data.
DELETE FROM event_log
For some scenarios, it might be the easiest to script out Table1, rename the existing Table1 to Table2 and run the script to recreate Table1.