Question

I have two MySQL tables with an one-to-many relationship between them. For example:

CREATE TABLE test1 (
    pk1 INTEGER AUTO_INCREMENT PRIMARY KEY,
    testvalue1 INTEGER
);

CREATE TABLE test2 (
    pk2 INTEGER AUTO_INCREMENT PRIMARY KEY,
    testvalue2 VARCHAR(50),
    fk2 INTEGER NOT NULL,
    FOREIGN KEY (fk2) REFERENCES test1 (pk1)
);

If I want to insert records in both tables I can first insert a record in the PK table (e.g. INSERT INTO test1 SET testvalue1=100), determine the PK value (e.g. SELECT MAX(pk1) AS LastId FROM test1 or use LAST_INSERT_ID())
and finally use that value to fill the FK column in the second table.

But is it possible to achieve this all in 1 command/query/action? So let’s MySQL fill in the PK- and FK-values using the AUTO INCREMENTs?

Answer 1

You should use two INSERT commands; or try to use an INSERT-trigger.

EDIT:

–An example with trigger:

CREATE TABLE dept(
  id INT(11) NOT NULL AUTO_INCREMENT,
  dept_name VARCHAR(255) DEFAULT NULL,
  PRIMARY KEY (id)
)
ENGINE = INNODB;

CREATE TABLE emp(
  id INT(11) NOT NULL AUTO_INCREMENT,
  emp_name VARCHAR(255) DEFAULT NULL,
  dept_id INT(11) DEFAULT NULL,
  PRIMARY KEY (id),
  CONSTRAINT FK_emp_dept_id FOREIGN KEY (dept_id)
  REFERENCES dept (id) ON DELETE RESTRICT ON UPDATE RESTRICT
)
ENGINE = INNODB;

DELIMITER $$

CREATE TRIGGER trigger1
AFTER INSERT
ON dept
FOR EACH ROW
BEGIN
  INSERT INTO emp VALUES (NULL, 'Someone', NEW.id);
END
$$

DELIMITER ;


-- Try to add new department.
INSERT INTO dept VALUES(NULL, 'Sales');

-- Is there new default employee?
SELECT * FROM emp;
+----+----------+---------+
| id | emp_name | dept_id |
+----+----------+---------+
|  1 | Someone  |       1 |
+----+----------+---------+