How to implement an auto_increment composite primary key with MySQL InnoDB? - mysql

Question

I have a table which has a composite primary key made up of one non-auto_increment column and one auto_increment column. The auto_increment column needs to increment individually for each of the non-auto_increment column values (more on this later). The storage engine is InnoDB. I don't wish to lock the table because of performance concerns. After inserting a value, a means to retrieve the last auto_increment value must be available.
The below script works at first, but the last INSERT results in id, checkingaccounts_id is 3, 2, but 1, 2 is desired. This is what I meant by The auto_increment column needs to increment individually for each of the non-auto_increment column values
Trigger and Stored Procedures are both acceptable, and so is a PHP/PDO application solution which somehow mimics the MySQL auto_increment behavior.
mysql> EXPLAIN checkingaccounts;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| data | varchar(45) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> EXPLAIN checks;
+---------------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| checkingaccounts_id | int(11) | NO | PRI | NULL | |
| data | varchar(45) | YES | | NULL | |
+---------------------+-------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
mysql> INSERT INTO checkingaccounts(id, data) VALUES(0,'bla');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO checkingaccounts(id, data) VALUES(0,'bla');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM checkingaccounts;
+----+------+
| id | data |
+----+------+
| 1 | bla |
| 2 | bla |
+----+------+
2 rows in set (0.00 sec)
mysql> INSERT INTO checks(id,checkingaccounts_id,data) VALUES(0,1,'bla');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO checks(id,checkingaccounts_id,data) VALUES(0,1,'bla');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM checks;
+----+---------------------+------+
| id | checkingaccounts_id | data |
+----+---------------------+------+
| 1 | 1 | bla |
| 2 | 1 | bla |
+----+---------------------+------+
2 rows in set (0.00 sec)
mysql> INSERT INTO checks(id,checkingaccounts_id,data) VALUES(0,2,'bla');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM checks;
+----+---------------------+------+
| id | checkingaccounts_id | data |
+----+---------------------+------+
| 1 | 1 | bla |
| 2 | 1 | bla |
| 3 | 2 | bla |
+----+---------------------+------+
3 rows in set (0.00 sec)
mysql>

Answer 1

Remove the auto_increment feature, try a stored procedure instead:
CREATE PROCEDURE insertChecks
(IN AccID int(9), IN data varchar(50))
BEGIN
DECLARE cid INT DEFAULT 1;
SELECT (COUNT(*) + 1) INTO cid
FROM checks
WHERE checkingaccounts_id = AccID;
INSERT INTO checks(id, checkingaccounts_id, data)
VALUES(cid, AccID, data);
END
And
call insertChecks(1,'bla');
call insertChecks(1,'bla');
call insertChecks(2,'bla');
Solution 2:
CREATE PROCEDURE insertChecks
(IN AccID int(9), IN data varchar(50))
BEGIN
INSERT INTO checks(id, checkingaccounts_id, data)
SELECT (COUNT(*) + 1), AccID, data
FROM checks
WHERE checkingaccounts_id = AccID;
END

Answer 2

Create a MyISAM table to create the auto_increment id only, and use a trigger to use this id for the targeted table. If there are more than one InnoDB tables that need a composite auto_incrementing primary key, add an extra primary key to the MyISAM table.
Disadvantages:
No foreign key constraints allowed on the MyISAM table, however, hopefully a trigger removes the risk.
Requires an additional table.
Advantages
Primary key valves are not reused if deleted.
Client just uses normal SQL queries and not a stored procedure.
Maybe less maintenance than a stored procedure since adding a column to a table doesn't require the trigger to be modified.
-- MySQL Script generated by MySQL Workbench
-- 07/08/16 05:12:11
-- Model: New Model Version: 1.0
SET #OLD_UNIQUE_CHECKS=##UNIQUE_CHECKS, UNIQUE_CHECKS=0;
SET #OLD_FOREIGN_KEY_CHECKS=##FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0;
SET #OLD_SQL_MODE=##SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES';
-- -----------------------------------------------------
-- Schema mydb
-- -----------------------------------------------------
CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci ;
USE `mydb` ;
-- -----------------------------------------------------
-- Table `mydb`.`a`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mydb`.`a` (
`id` INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`))
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `mydb`.`t1`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mydb`.`t1` (
`a_id` INT NOT NULL,
`id` INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`, `a_id`),
CONSTRAINT `fk_t1_a1`
FOREIGN KEY (`a_id`)
REFERENCES `mydb`.`a` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `mydb`.`t2`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mydb`.`t2` (
`a_id` INT NOT NULL,
`id` INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`, `a_id`),
CONSTRAINT `fk_t2_a1`
FOREIGN KEY (`a_id`)
REFERENCES `mydb`.`a` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `mydb`.`t3`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mydb`.`t3` (
`a_id` INT NOT NULL,
`id` INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`, `a_id`),
CONSTRAINT `fk_t3_a1`
FOREIGN KEY (`a_id`)
REFERENCES `mydb`.`a` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `mydb`.`inc`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `mydb`.`inc` (
`a_id` INT NOT NULL,
`id` INT NOT NULL AUTO_INCREMENT,
`type` CHAR(4) NOT NULL,
PRIMARY KEY (`a_id`, `type`, `id`))
ENGINE = MyISAM;
SET SQL_MODE=#OLD_SQL_MODE;
SET FOREIGN_KEY_CHECKS=#OLD_FOREIGN_KEY_CHECKS;
SET UNIQUE_CHECKS=#OLD_UNIQUE_CHECKS;
USE `mydb`;
DELIMITER $$
USE `mydb`$$
CREATE TRIGGER `t1_BINS` BEFORE INSERT ON `t1` FOR EACH ROW
BEGIN
INSERT INTO inc(a_id,type) VALUES(NEW.a_id,'t1');
SET NEW.id=LAST_INSERT_ID();
END$$
USE `mydb`$$
CREATE TRIGGER `t2_BINS` BEFORE INSERT ON `t2` FOR EACH ROW
BEGIN
INSERT INTO inc(a_id,type) VALUES(NEW.a_id,'t2');
SET NEW.id=LAST_INSERT_ID();
END$$
USE `mydb`$$
CREATE TRIGGER `t3_BINS` BEFORE INSERT ON `t3` FOR EACH ROW
BEGIN
INSERT INTO inc(a_id,type) VALUES(NEW.a_id,'t3');
SET NEW.id=LAST_INSERT_ID();
END$$
DELIMITER ;
Testing
mysql> insert into a(id) VALUES(null);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t1(a_id) VALUES(1);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM t1;
+------+----+
| a_id | id |
+------+----+
| 1 | 1 |
+------+----+
1 row in set (0.00 sec)
mysql> insert into t1(a_id) VALUES(1);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t1(a_id) VALUES(1);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM t1;
+------+----+
| a_id | id |
+------+----+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
+------+----+
3 rows in set (0.00 sec)
mysql> insert into t2(a_id) VALUES(1);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM t2;
+------+----+
| a_id | id |
+------+----+
| 1 | 1 |
+------+----+
1 row in set (0.00 sec)
mysql> insert into a(id) VALUES(null);
Query OK, 1 row affected (0.00 sec)
mysql> insert into a(id) VALUES(null);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t1(a_id) VALUES(2);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t1(a_id) VALUES(3);
Query OK, 1 row affected (0.00 sec)
mysql> insert into t1(a_id) VALUES(1);
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM t1;
+------+----+
| a_id | id |
+------+----+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 1 |
| 3 | 1 |
+------+----+
6 rows in set (0.00 sec)
mysql>