MySQL insert into Statement Exercises: Insert rows into the table employees in which a set of columns department_id and manager_id contains a unique value and that combined values must have exists into the table departments

MySQL insert into Statement: Exercise-14 with Solution

14. Write a SQL statement to insert rows into the table employees in which a set of columns department_id and manager_id contains a unique value and that combined values must have exists into the table departments.

Sample table departments.


CREATE TABLE IF NOT EXISTS departments ( 
DEPARTMENT_ID integer NOT NULL UNIQUE, 
DEPARTMENT_NAME varchar(30) NOT NULL, 
MANAGER_ID integer DEFAULT NULL, 
LOCATION_ID integer DEFAULT NULL, 
PRIMARY KEY (DEPARTMENT_ID) 
)ENGINE=InnoDB;


INSERT INTO departments VALUES(60,'SALES',201,89);
INSERT INTO departments VALUES(61,'ACCOUNTS',201,89);


mysql> SELECT * FROM departments;
+---------------+-----------------+------------+-------------+
| DEPARTMENT_ID | DEPARTMENT_NAME | MANAGER_ID | LOCATION_ID |
+---------------+-----------------+------------+-------------+
|            60 | SALES           |        201 |          89 |
|            61 | ACCOUNTS        |        201 |          89 |
+---------------+-----------------+------------+-------------+
2 rows in set (0.00 sec)

Sample table jobs.

CREATE TABLE IF NOT EXISTS jobs ( 
JOB_ID integer NOT NULL UNIQUE PRIMARY KEY, 
JOB_TITLE varchar(35) NOT NULL DEFAULT ' ', 
MIN_SALARY decimal(6,0) DEFAULT 8000, 
MAX_SALARY decimal(6,0) DEFAULT 20000
)ENGINE=InnoDB;


INSERT INTO jobs(JOB_ID,JOB_TITLE) VALUES(1001,'OFFICER');
INSERT INTO jobs(JOB_ID,JOB_TITLE) VALUES(1002,'CLERK');

mysql> SELECT * FROM jobs;
+--------+-----------+------------+------------+
| JOB_ID | JOB_TITLE | MIN_SALARY | MAX_SALARY |
+--------+-----------+------------+------------+
|   1001 | OFFICER   |       8000 |      20000 |
|   1002 | CLERK     |       8000 |      20000 |
+--------+-----------+------------+------------+
2 rows in set (0.00 sec)


Sample table employees.

CREATE TABLE IF NOT EXISTS employees ( 
EMPLOYEE_ID integer NOT NULL PRIMARY KEY, 
FIRST_NAME varchar(20) DEFAULT NULL, 
LAST_NAME varchar(25) NOT NULL, 
DEPARTMENT_ID integer DEFAULT NULL, 
FOREIGN KEY(DEPARTMENT_ID) 
REFERENCES  departments(DEPARTMENT_ID),
JOB_ID integer NOT NULL, 
FOREIGN KEY(JOB_ID) 
REFERENCES  jobs(JOB_ID),
SALARY decimal(8,2) DEFAULT NULL
)ENGINE=InnoDB;

Now insert the rows into the table employees.

Sample Solution:

INSERT INTO employees VALUES(510,'Alex','Hanes',60,1001,18000);

Let execute the above code in MySQL 5.6 command prompt.

Here is the structure of the table:

mysql> SELECT * FROM employees;
+-------------+------------+-----------+---------------+--------+----------+
| EMPLOYEE_ID | FIRST_NAME | LAST_NAME | DEPARTMENT_ID | JOB_ID | SALARY   |
+-------------+------------+-----------+---------------+--------+----------+
|         510 | Alex       | Hanes     |            60 |   1001 | 18000.00 |
+-------------+------------+-----------+---------------+--------+----------+
1 row in set (0.00 sec)

Here in the above insert statement the child column department_id and job_id of child table employees are successfully referencing with the department_id and job_id column of parent tables departments and jobs respectively, so no problem have been arisen to the insertion.

Now insert another row in the employees table.

INSERT INTO employees VALUES(511,'Tom','Elan',60,1003,22000);

Let execute the above code in MySQL 5.6 command prompt.

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`hrr`.`employees`, CONSTRAINT `employees_ibfk_2` FORE
OB_ID`) REFERENCES `jobs` (`JOB_ID`))

Here in the above insert statement show that, within child columns department_id and job_id of child table employees, the department_id are successfully referencing with the department_id of parent table departments but job_id column are not successfully referencing with the job_id of parent table jobs, so the problem have been arisen to the insertion displayed an error message.

Now insert another row in the employees table.

INSERT INTO employees VALUES(511,'Tom','Elan',80,1001,22000);

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`hrr`.`employees`, CONSTRAINT `employees_ibfk_2` FOREIGN KEY (`J
OB_ID`) REFERENCES `jobs` (`JOB_ID`))

Here in the above insert statement show that, within child columns department_id and job_id of child table employees, the job_id are successfully referencing with the job_id of parent table jobs but department_id column are not successfully referencing with the department_id of parent table departments, so the problem have been arisen to the insertion and displayed the error message.

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