I want a table maximum rows to 100, If i add 101 row to that table, the 1 row should delete automatically. likewise i just want table total row count to 100, delete order should be FIFO.
Is there any direct MySQL function for that?
Use BEFORE INSERT trigger for this.
Below, I kept limit of 25, set according to your need.
DELIMITER $$
CREATE TRIGGER trigger1
BEFORE INSERT
ON table1
FOR EACH ROW
BEGIN
SELECT COUNT(*) INTO #cnt FROM table1;
IF #cnt >= 25 THEN
CALL sth(); -- raise an error
END IF;
END
$$
DELIMITER ;
You can a simple trigger like below:
CREATE TRIGGER Deleter AFTER INSERT on YourTable FOR EACH ROW
BEGIN
Delete from yourTable where ID = (Select MIN(id) from yourTable);
END;
Same as :
How do you make a threshold or limit mysql table?
Related
How do I limit the total column to 10 columna and total rows to 500 data per table in Mysql
Like P.Salmon suggested,we can restrict users from altering table structures. This can be done by revoking their ALTER privilege on said tables. e.g revoke alter on testdb.thistable from thisuser; As to limit the total rows , we can use a trigger to check the existing row number every time a new row is to be inserted. If the limit is reached, abort the INSERT as well as raise a warning. The trigger looks like this:
delimiter //
drop trigger if exists check_row_limit ;
create trigger check_row_limit before insert on thistable for each row
begin
if (select count(*) from thistable) >= 500 then
signal SQLSTATE VALUE '99999' SET MESSAGE_TEXT = 'The number of rows has reached the limit. INSERT fails. ';
end if;
end//
delimiter ;
Can we perform count operation inside a trigger?
I have a table TB1 with fields id,title,author,date. I want to create a trigger that when ever I will insert a row in tb1. A trigger should run and the total no of authors in the tb1 should show in a new table total.
I have written the code
DELIMITER $$
CREATE TRIGGER insertintonew2
AFTER
INSERT ON tb1
FOR EACH ROW
BEGIN
UPDATE total
SET total_author = (select count(*) from tb1);
END;
$$
The output I am getting a is populated with total_author column name but the count value is not populated.
Can anyone tell me why is it happening?
I want to add a limit to how many items my table can have. I want the maximum amount of items to be 10. I want it to only be 10 people in my table. I dont want it to be able to add items after the 10th person. Here is my code:
CREATE TABLE person (
name VARCHAR(233) NOT NULL,
number int NOT NULL AUTO_INCREMENT,
PRIMARY KEY(number),
Check(number>10))
delimiter //
create trigger limit_persons before insert on person for each row
begin
declare count integer
select COUNT(*) FROM person INTO count;
if count>=10 then
signal sqlstate '45000' set message_text = 'Limit exceeded';
end if;
end
//
I would advise to handle such stuff as limitations in the software itself. So you have control over it later and it is overall a cleaner solution. But you can try this, if you really want to limit it in mysql:
ALTER TABLE tbl_name MAX_ROWS=10 AVG_ROW_LENGTH=nnn;
You can also check out triggers and signals:
https://dev.mysql.com/doc/refman/5.5/en/signal.html
https://dev.mysql.com/doc/refman/5.5/en/trigger-syntax.html
You can set up a trigger (to be specific, an Insert trigger) that counts the records and, if count is more than 10, it does not allow the insert operation.
Following code will be helpful to you,
DELIMITER $$
CREATE TRIGGER LimitRowCountTrigger
BEFORE INSERT
ON person
FOR EACH ROW
BEGIN
SELECT COUNT(*) INTO #cnt FROM person;
IF #cnt > 10 THEN
CALL sth(); -- raise an error
END IF;
END
$$
DELIMITER ;
I have three columns column 1, column 2, column 3(total). i want to put the sum of column 1 and column 2 into column 3 after every update query..... note i am using code igniter.. how can i do it if i update col 1 then total column automatically update itself.
Try like this:
DELIMITER $$
CREATE TRIGGER updtrigger AFTER UPDATE ON mytable
FOR EACH ROW
BEGIN
IF NEW.col1 <> OLD.col1 OR NEW.col2 <> OLD.col2 THEN
SET NEW.col3 = NEW.col1 + New.col2;
END IF;
END $$
Here is a very good tutorial.
An AFTER UPDATE Trigger means that MySQL will fire this trigger after
the UPDATE operation is executed.
why dont you just update the db instead of creating a trigger. plus youve created the trigger after the insert, it should go before. but really you shouldn't be doing it that way
try this code:
DELIMITER $$
CREATE
TRIGGER `db_name`.`trigger_name` AFTER UPDATE
ON `db_name`.`table_name`
FOR EACH ROW BEGIN
UPDATE
`table_name`
SET
`column3` = `column1` + `column2`;
END$$
DELIMITER ;
I would like to limit the size of a table to X rows (I'll use 5 for example). When the limit is reached, I want to copy the oldest row to another table, then delete it. I currently have:
CREATE TRIGGER LimitRows BEFORE INSERT ON MyTable
FOR EACH ROW BEGIN
IF (SELECT COUNT(*) FROM MyTable) >= 5 THEN
INSERT INTO HistoryTable
SELECT *
FROM MyTable A
WHERE vhID = A.min(vhID);
DELETE FROM MyTable
WHERE vhID = min(vhID);
END IF;
END;
Currently, I get the error:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 8
How do I write this trigger correctly? Also, how can I modify to cut the table down to 5 rows if it starts out at something like 100 rows?
You need to change the delimiter first
delimiter |
CREATE TRIGGER LimitRows BEFORE INSERT ON MyTable
FOR EACH ROW BEGIN
IF (SELECT COUNT(*) FROM MyTable) >= 5 THEN
INSERT INTO HistoryTable
SELECT *
FROM MyTable A
WHERE vhID = A.min(vhID);
DELETE FROM MyTable
WHERE vhID = min(vhID);
END IF;
END
|
delimiter ;
Otherwise the trigger definition would end at the first ; which would make it incomplete.