[MDEV-6259] DELETE with OFFSET Created: 2014-05-22  Updated: 2015-11-17

Status: Open
Project: MariaDB Server
Component/s: None
Fix Version/s: None

Type: Task Priority: Major
Reporter: roberto spadim Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: None


 Description   

Allow DELETE statment with OFFSET, this allow a DELETE like SQLITE:
http://www.sqlite.org/lang_delete.html

it's interesting with history table applications where a fixed number of rows is wanted, for example

CREATE TABLE history (
 
 channel_id INT NOT NULL DEFAULT 0,
 
 date_unix DECIMAL(22,6) NOT NULL DEFAULT 0,
 
 value DECIMAL(22,7) NOT NULL DEFAULT 0,
 
 PRIMARY KEY (channel_id,date_unix)
 
);

many inserts....

INSERT INTO history (1,now(),current_temperature);
 
INSERT INTO history (1,now(),current_temperature);
 
INSERT INTO history (1,now(),current_temperature);
 
INSERT INTO history (1,now(),current_temperature);
 
.....

an crond job executed at every hour:

DELETE FROM history WHERE channel_id=1 ORDER BY date_unix DESC LIMIT -1 OFFSET 5000

from SQLITE: A negative LIMIT value is interpreted as "no limit".

this will remove all rows from this 'channel' that are older than the 5000th row

—
today this should be done with two queries:

SELECT date_unix FROM history WHERE channel_id=1 ORDER BY date_unix DESC LIMIT 1 OFFSET 5000

get the date_unix value, and execute:

DELETE FROM history WHERE channel_id=1 AND date_unix<"{$date_unix from previous query$}"


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