I want to write an oracle sql query to keep first three latest records ordered by TIMESTAMP and delete the rest for each MACHINE_ID.
I want to know how efficient i can do that. Hope you understand my question!!
Below is the table for example. All the records with USERFILE = 0 can be filtered out in the sql query.
**Result after - group by MACHINE_ID and sort by TIMESTAMP desc **
After leaving the first 3 latest records per MACHINE_ID and deleting the oldest records, final result should be
One method is:
delete from t
where t.timestamp not in (select t2.timestamp
from t t2
where t2.machine_id = t.machine_id
order by t2.timestamp desc
fetch first 3 rows only
);
For performance, you want an index on (machine_id, timestamp desc).
You can number the rows per machine and then delete all rows with a number greater than 3. Ideally we could simply delete from a query, but I'm getting ORA-01732: data manipulation operation not legal on this view when trying this in Oracle 19c.
We need two steps hence:
find the rows
delete the rows
The statement using rowid to acces the rows again quickly:
delete from mytable
where rowid in
(
select rowid
from
(
select
rowid,
row_number() over (partition by machine_id order by timestamp desc) as rn
from mytable
)
where rn > 3
);
I want to delete the last 1000 records in my sqlite DB.
The following statement executes with no errors, but deletes (affects) all records.
I use the following SQL statement:
DELETE FROM LOGS WHERE (SELECT ROWID FROM LOGS ORDER BY ROWID DESC LIMIT 1000)
Any ideas?
First check the sub-query return the last 1000 records
SELECT ROWID FROM LOGS ORDER BY ROWID DESC LIMIT 1000
If it returns the correct result, could you try the below query. I added ROWID IN in the WHERE clause
DELETE FROM LOGS WHERE ROWID IN (SELECT ROWID FROM LOGS ORDER BY ROWID DESC LIMIT 1000)
I have a SQL Server database table : History_KH
It look like:
Now I want to limit row number of this table (ex : 200 rows)
And when I insert new rows from code, It will insert on top of table. That's mean : Insert new rows on top of database table and the old rows over of 200 counts will be delete.
Please support me.
You can't really limit a table for a fix number of records but you can get rid of unwanted records. Assuming you are on SQL-Server
--STEP1 :Do your insert here
--STEP2: Delete older records over 200 ordering by dateTime column
;WITH CTE AS (
SELECT *, ROW_NUMBER() OVER (ORDER BY DateTime DESC) rn
FROM YourTable
)
DELETE CTE WHERE rn > 200
You didn't even post what database you are using. I'm assuming mysql.
Assuming you want to order by Datetime and Username is unique, use this update...
update `History_KH` set `Username` = $myUser, `Datetime` = $myDatetime,
`Datechange` = $myDatechange, `Value` = $myValue where `Username` in
(select `Username` from `History_KH` order by `Datetime` limit 200)
I am cleaning out a database table without a primary key (I know, I know, what were they thinking?). I cannot add a primary key, because there is a duplicate in the column that would become the key. The duplicate value comes from one of two rows that are in all respects identical. I can't delete the row via a GUI (in this case MySQL Workbench, but I'm looking for a database agnostic approach) because it refuses to perform tasks on tables without primary keys (or at least a UQ NN column), and I cannot add a primary key, because there is a duplicate in the column that would become the key. The duplicate value comes from one...
How can I delete one of the twins?
SET ROWCOUNT 1
DELETE FROM [table] WHERE ....
SET ROWCOUNT 0
This will only delete one of the two identical rows
One option to solve your problem is to create a new table with the same schema, and then do:
INSERT INTO new_table (SELECT DISTINCT * FROM old_table)
and then just rename the tables.
You will of course need approximately the same amount of space as your table requires spare on your disk to do this!
It's not efficient, but it's incredibly simple.
Note that MySQL has its own extension of DELETE, which is DELETE ... LIMIT, which works in the usual way you'd expect from LIMIT: http://dev.mysql.com/doc/refman/5.0/en/delete.html
The MySQL-specific LIMIT row_count option to DELETE tells the server
the maximum number of rows to be deleted before control is returned to
the client. This can be used to ensure that a given DELETE statement
does not take too much time. You can simply repeat the DELETE
statement until the number of affected rows is less than the LIMIT
value.
Therefore, you could use DELETE FROM some_table WHERE x="y" AND foo="bar" LIMIT 1; note that there isn't a simple way to say "delete everything except one" - just keep checking whether you still have row duplicates.
delete top(1) works on Microsoft SQL Server (T-SQL).
This can be accomplished using a CTE and the ROW_NUMBER() function, as below:
/* Sample Data */
CREATE TABLE #dupes (ID INT, DWCreated DATETIME2(3))
INSERT INTO #dupes (ID, DWCreated) SELECT 1, '2015-08-03 01:02:03.456'
INSERT INTO #dupes (ID, DWCreated) SELECT 2, '2014-08-03 01:02:03.456'
INSERT INTO #dupes (ID, DWCreated) SELECT 1, '2013-08-03 01:02:03.456'
/* Check sample data - returns three rows, with two rows for ID#1 */
SELECT * FROM #dupes
/* CTE to give each row that shares an ID a unique number */
;WITH toDelete AS
(
SELECT ID, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY DWCreated) AS RN
FROM #dupes
)
/* Delete any row that is not the first instance of an ID */
DELETE FROM toDelete WHERE RN > 1
/* Check the results: ID is now unique */
SELECT * FROM #dupes
/* Clean up */
DROP TABLE #dupes
Having a column to ORDER BY is handy, but not necessary unless you have a preference for which of the rows to delete. This will also handle all instances of duplicate records, rather than forcing you to delete one row at a time.
For PostgreSQL you can do this:
DELETE FROM tablename
WHERE id IN (SELECT id
FROM (SELECT id, ROW_NUMBER()
OVER (partition BY column1, column2, column3 ORDER BY id) AS rnum
FROM tablename) t
WHERE t.rnum > 1);
column1, column2, column3 would the column set which have duplicate values.
Reference here.
This works for PostgreSQL
DELETE FROM tablename WHERE id = 123 AND ctid IN (SELECT ctid FROM tablename WHERE id = 123 LIMIT 1)
Tried LIMIT 1? This will only delete 1 of the rows that match your DELETE query
DELETE FROM `table_name` WHERE `column_name`='value' LIMIT 1;
In my case I could get the GUI to give me a string of values of the row in question (alternatively, I could have done this by hand). On the suggestion of a colleague, in whose debt I remain, I used this to create an INSERT statement:
INSERT
'ID1219243408800307444663', '2004-01-20 10:20:55', 'INFORMATION', 'admin' (...)
INTO some_table;
I tested the insert statement, so that I now had triplets. Finally, I ran a simple DELETE to remove all of them...
DELETE FROM some_table WHERE logid = 'ID1219243408800307444663';
followed by the INSERT one more time, leaving me with a single row, and the bright possibilities of a primary key.
in case you can add a column like
ALTER TABLE yourtable ADD IDCOLUMN bigint NOT NULL IDENTITY (1, 1)
do so.
then count rows grouping by your problem column where count >1 , this will identify your twins (or triplets or whatever).
then select your problem column where its content equals the identified content of above and check the IDs in IDCOLUMN.
delete from your table where IDCOLUMN equals one of those IDs.
You could use a max, which was relevant in my case.
DELETE FROM [table] where id in
(select max(id) from [table] group by id, col2, col3 having count(id) > 1)
Be sure to test your results first and having a limiting condition in your "having" clausule. With such a huge delete query you might want to update your database first.
delete top(1) tableNAme
where --your conditions for filtering identical rows
I added a Guid column to the table and set it to generate a new id for each row. Then I could delete the rows using a GUI.
In PostgreSQL there is an implicit column called ctid. See the wiki. So you are free to use the following:
WITH cte1 as(
SELECT unique_column, max( ctid ) as max_ctid
FROM table_1
GROUP BY unique_column
HAVING count(*) > 1
), cte2 as(
SELECT t.ctid as target_ctid
FROM table_1 t
JOIN cte1 USING( unique_column )
WHERE t.ctid != max_ctid
)
DELETE FROM table_1
WHERE ctid IN( SELECT target_ctid FROM cte2 )
I'm not sure how safe it is to use this when there is a possibility of concurrent updates. So one may find it sensible to make a LOCK TABLE table_1 IN ACCESS EXCLUSIVE MODE; before actually doing the cleanup.
In case there are multiple duplicate rows to delete and all fields are identical, no different id, the table has no primary key , one option is to save the duplicate rows with distinct in a new table, delete all duplicate rows and insert the rows back. This is helpful if the table is really big and the number of duplicate rows is small.
--- col1 , col2 ... coln are the table columns that are relevant.
--- if not sure add all columns of the table in the select bellow and the where clause later.
--- make a copy of the table T to be sure you can rollback anytime , if possible
--- check the ##rowcount to be sure it's what you want
--- use transactions and rollback in case there is an error
--- first find all with duplicate rows that are identical , this statement could be joined
--- with the first one if you choose all columns
select col1,col2, --- other columns as needed
count(*) c into temp_duplicate group by col1,col2 having count(*) > 1
--- save all the rows that are identical only once ( DISTINCT )
insert distinct * into temp_insert from T , temp_duplicate D where
T.col1 = D.col1 and
T.col2 = D.col2 --- and other columns if needed
--- delete all the rows that are duplicate
delete T from T , temp_duplicate D where
T.col1 = D.col1 and
T.col2 = D.col2 ---- and other columns if needed
--- add the duplicate rows , now only once
insert into T select * from temp_insert
--- drop the temp tables after you check all is ok
If, like me, you don't want to have to list out all the columns of the database, you can convert each row to JSONB and compare by that.
(NOTE: This is incredibly inefficient - be careful!)
select to_jsonb(a.*), to_jsonb(b.*)
FROM
table a
left join table b
on
a.entry_date < b.entry_date
where (SELECT NOT exists(
SELECT
FROM jsonb_each_text(to_jsonb(a.*) - 'unwanted_column') t1
FULL OUTER JOIN jsonb_each_text(to_jsonb(b.*) - 'unwanted_column') t2 USING (key)
WHERE t1.value<>t2.value OR t1.key IS NULL OR t2.key IS NULL
))
Suppose we want to delete duplicate records with keeping only 1 unique records from Employee table - Employee(id,name,age)
delete from Employee
where id not in (select MAX(id)
from Employee
group by (id,name,age)
);
You can use limit 1
This works perfectly for me with MySQL
delete from `your_table` [where condition] limit 1;
DELETE FROM Table_Name
WHERE ID NOT IN
(
SELECT MAX(ID) AS MaxRecordID
FROM Table_Name
GROUP BY [FirstName],
[LastName],
[Country]
);
We have a table that has had the same data inserted into it twice by accident meaning most (but not all) rows appears twice in the table. Simply put, I'd like an SQL statement to delete one version of a row while keeping the other; I don't mind which version is deleted as they're identical.
Table structure is something like:
FID, unique_ID, COL3, COL4....
Unique_ID is the primary key, meaning each one appears only once.
FID is a key that is unique to each feature, so if it appears more than once then the duplicates should be deleted.
To select features that have duplicates would be:
select count(*) from TABLE GROUP by FID
Unfortunately I can't figure out how to go from that to a SQL delete statement that will delete extraneous rows leaving only one of each.
This sort of question has been asked before, and I've tried the create table with distinct, but how do I get all columns without naming them? This only gets the single column FID and itemising all the columns to keep gives an: ORA-00936: missing expression
CREATE TABLE secondtable NOLOGGING as select distinct FID from TABLE
If you don't care which row is retained
DELETE FROM your_table_name a
WHERE EXISTS( SELECT 1
FROM your_table_name b
WHERE a.fid = b.fid
AND a.unique_id < b.unique_id )
Once that's done, you'll want to add a constraint to the table that ensures that FID is unique.
Try this
DELETE FROM table_name A WHERE ROWID > (
SELECT min(rowid) FROM table_name B
WHERE A.FID = B.FID)
A suggestion
DELETE FROM x WHERE ROWID IN
(WITH y AS (SELECT xCOL, MIN(ROWID) FROM x GROUP BY xCOL HAVING COUNT(xCOL) > 1)
SELCT a.ROWID FROM x, y WHERE x.XCOL=y.XCOL and x.ROWIDy.ROWID)
Try with this.
DELETE FROM firsttable WHERE unique_ID NOT IN
(SELECT MAX(unique_ID) FROM firsttable GROUP BY FID)
EDIT:
One explanation:
SELECT MAX(unique_ID) FROM firsttable GROUP BY FID;
This sql statement will pick each maximum unique_ID row from each duplicate rows group. And delete statement will keep these maximum unique_ID rows and delete other rows of each duplicate group.
You can try this.
delete from tablename a
where a.logid, a.pointid, a.routeid) in (select logid, pointid, routeid from tablename
group by logid, pointid, routeid having count(*) > 1)
and rowid not in (select min(rowid) from tablename
group by logid, pointid, routeid having count(*) > 1)