Mysql – How to make MySQL 8 alert when integer overflow happens during INSERT … ON DUPLICATE KEY

error handlingintegerMySQLmysql-8.0

Let's consider we have a simple table with auto-incrementing integer ID and some unique column:

CREATE TABLE `test` (
  `id` int unsigned NOT NULL AUTO_INCREMENT,
  `value` tinyint DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `value` (`value`)
);

Imagine we inserted into it so many times that ID reached the maximum:

INSERT INTO test VALUES 
(4294967294, 1),
(4294967295, 2);

Now we are trying to insert one more row and if it's duplicate then change the value to 3:

INSERT INTO test (`value`) VALUES (1) ON DUPLICATE KEY UPDATE `value` = 3;

What is the expected behaviour?

        id     value  
----------  --------
4294967294         3
4294967295         2

What we get in fact:

        id     value  
----------  --------
4294967294         1
4294967295         3

How? Because of the integer overflow the auto-generated ID of the new row was again 4294967295.

So now the question. Is it possible to make MySQL 8 alert if the overflow happens during query? In my case such silent overflow caused huge data loss. Because all newly added rows just overwrote the last row.

PS I'm not asking how to fix or prevent such overflow. That's obvious. I'm asking exactly how to catch such errors.

Best Answer

USE a BEFORE INSERT TRIGGER to check for all fields where you can reach their limits.

With the newest mysql incarnation you can actually can use the CKECK CONSTRAINT to prevent an INSERT at all, but with the TRIGGER you can manage and define What to do

Related Solutions

Mysql – Drop auto increment hack w/o alter table

I tried something similar just now

Here is MySQL for My PC

mysql> select * from information_schema.global_variables where variable_name='datadir' or variable_name like 'versio%';
+-------------------------+------------------------------+
| VARIABLE_NAME           | VARIABLE_VALUE               |
+-------------------------+------------------------------+
| VERSION_COMMENT         | MySQL Community Server (GPL) |
| VERSION                 | 5.5.12-log                   |
| VERSION_COMPILE_MACHINE | x86                          |
| DATADIR                 | C:\MySQL_5.5.12\data\        |
| VERSION_COMPILE_OS      | Win64                        |
+-------------------------+------------------------------+
5 rows in set (0.00 sec)

I will run this using MyISAM

Step 01) create a table called 'rolando'
Step 02) insert 'dominique' and 'diamond'
Step 03) copy the table structure to 'pamela'
Step 04) alter 'pamela' to not have auto_increment
Step 05) In DOS, copy rolando.MYD to pamela.MYD
Step 06) run REPAIR TABLE pamela; (Rebuild pamela.MYI)
Step 07) run SELECT COUNT(1) FROM pamela;
Step 08) run SHOW CREATE TABLE pamela\G
Step 09) run SELECT * FROM pamela;
Step 10) insert 'carlik' into pamela
Step 11) run SELECT * FROM pamela;

Let's see if these steps are kosher.

Here are Steps 1-4

mysql> drop table if exists rolando;
Query OK, 0 rows affected (0.02 sec)

mysql> drop table if exists pamela;
Query OK, 0 rows affected (0.00 sec)

mysql> create table rolando
    -> (
    ->     name varchar(20),
    ->     id int not null auto_increment,
    ->     primary key (id)
    -> ) ENGINE=MyISAM;
Query OK, 0 rows affected (0.05 sec)

mysql> insert into rolando (name) values ('dominique'),('diamond');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from rolando;
+-----------+----+
| name      | id |
+-----------+----+
| dominique |  1 |
| diamond   |  2 |
+-----------+----+
2 rows in set (0.00 sec)

mysql> create table pamela like rolando;
Query OK, 0 rows affected (0.05 sec)

mysql> show create table rolando\G
*************************** 1. row ***************************
       Table: rolando
Create Table: CREATE TABLE `rolando` (
  `name` varchar(20) DEFAULT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> show create table pamela\G
*************************** 1. row ***************************
       Table: pamela
Create Table: CREATE TABLE `pamela` (
  `name` varchar(20) DEFAULT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.02 sec)

mysql> alter table pamela modify id int(11) unsigned not null;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table pamela\G
*************************** 1. row ***************************
       Table: pamela
Create Table: CREATE TABLE `pamela` (
  `name` varchar(20) DEFAULT NULL,
  `id` int(11) unsigned NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> select count(1) from pamela;
+----------+
| count(1) |
+----------+
|        0 |
+----------+
1 row in set (0.01 sec)

mysql>

Here is Step 6

C:\>copy C:\MySQL_5.5.12\data\test\rolando.MYD C:\MySQL_5.5.12\data\test\pamela.MYD
        1 file(s) copied.

C:\>

Here are the rest of the Steps starting at Step 7

mysql> repair table pamela;
+-------------+--------+----------+------------------------------------+
| Table       | Op     | Msg_type | Msg_text                           |
+-------------+--------+----------+------------------------------------+
| test.pamela | repair | warning  | Number of rows changed from 0 to 2 |
| test.pamela | repair | status   | OK                                 |
+-------------+--------+----------+------------------------------------+
2 rows in set (0.03 sec)

mysql> select count(1) from pamela;
+----------+
| count(1) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)

mysql> insert into pamela (name,id) values ('carlik',3);
Query OK, 1 row affected (0.00 sec)

mysql> select * from pamela;
+-----------+----+
| name      | id |
+-----------+----+
| dominique |  1 |
| diamond   |  2 |
| carlik    |  3 |
+-----------+----+
3 rows in set (0.00 sec)

mysql>

Dangerous game, isn't it ???

Guess what? Stuff like this is actually published in "High Performance MySQL : Optimization, Backups, Replication, and more", Pages 146-148 under the Subheading Speeding Up ALTER TABLE. Page 147 Paragraph 1 says:

The technique we are about to demonstrate is unsupported, undocumented, and may not work. Use it at your risk. We advise you to back up you data first!

I also had an earlier post when someone ask a similar question : Can I rename the values in a MySQL ENUM column in one query?

You got guts, @atxdba !!!

Mysql – Trouble with triggers and insert .. on duplicate key update

This question came back on my radar after a recent comment was posted.

This issue at the time turned out to be this reporting table that was meant to be maintained by triggers was on a slave only.

The insert on duplicate key statements were getting flagged as not safe for statement based replication and getting pushed through in RBR (the stream was in mixed mode).

RBR events do not fire triggers.

Best Answer

Related Solutions

Mysql – Drop auto increment hack w/o alter table

Mysql – Trouble with triggers and insert .. on duplicate key update

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