PostgreSQL Create Table: Create a table to allow one of the columns to contain unique values and the combination of another two are referencing to the column combination of another table
14. Write a SQL statement to create a table employees, including employee_id, first_name, last_name, email, phone_number hire_date, job_id, salary, commission, manager_id and department_id and make sure that, the employee_id column did not contain any duplicate values at the time of insertion and the foreign key columns combined by department_id and manager_id columns contain only those unique combination values, which combinations exist in the departments table.
Assume the structure of departments table below.
Indexes:
"departments_pkey" PRIMARY KEY, btree (department_id, manager_id)
Sample Solution:
Code:
CREATE TABLE IF NOT EXISTS employees (
EMPLOYEE_ID decimal(6,0) NOT NULL PRIMARY KEY,
FIRST_NAME varchar(20) DEFAULT NULL,
LAST_NAME varchar(25) NOT NULL,
EMAIL varchar(25) NOT NULL,
PHONE_NUMBER varchar(20) DEFAULT NULL,
HIRE_DATE date NOT NULL,
JOB_ID varchar(10) NOT NULL,
SALARY decimal(8,2) DEFAULT NULL,
COMMISSION_PCT decimal(2,2) DEFAULT NULL,
MANAGER_ID decimal(6,0) DEFAULT NULL,
DEPARTMENT_ID decimal(4,0) DEFAULT NULL,
FOREIGN KEY(DEPARTMENT_ID,MANAGER_ID)
REFERENCES departments(DEPARTMENT_ID,MANAGER_ID)
);
Output:
postgres=# CREATE TABLE IF NOT EXISTS employees ( postgres(# EMPLOYEE_ID decimal(6,0) NOT NULL PRIMARY KEY, postgres(# FIRST_NAME varchar(20) DEFAULT NULL, postgres(# LAST_NAME varchar(25) NOT NULL, postgres(# EMAIL varchar(25) NOT NULL, postgres(# PHONE_NUMBER varchar(20) DEFAULT NULL, postgres(# HIRE_DATE date NOT NULL, postgres(# JOB_ID varchar(10) NOT NULL, postgres(# SALARY decimal(8,2) DEFAULT NULL, postgres(# COMMISSION_PCT decimal(2,2) DEFAULT NULL, postgres(# MANAGER_ID decimal(6,0) DEFAULT NULL, postgres(# DEPARTMENT_ID decimal(4,0) DEFAULT NULL, postgres(# FOREIGN KEY(DEPARTMENT_ID,MANAGER_ID) postgres(# REFERENCES departments(DEPARTMENT_ID,MANAGER_ID)); CREATE TABLE
Here is the command to see the structure of the created table :
postgres=# \d employees
Table "public.employees"
Column | Type | Modifiers
----------------+-----------------------+---------------------------------
employee_id | numeric(6,0) | not null
first_name | character varying(20) | default NULL::character varying
last_name | character varying(25) | not null
email | character varying(25) | not null
phone_number | character varying(20) | default NULL::character varying
hire_date | date | not null
job_id | character varying(10) | not null
salary | numeric(8,2) | default NULL::numeric
commission_pct | numeric(2,2) | default NULL::numeric
manager_id | numeric(6,0) | default NULL::numeric
department_id | numeric(4,0) | default NULL::numeric
Indexes:
"employees_pkey" PRIMARY KEY, btree (employee_id)
Foreign-key constraints:
"employees_department_id_fkey" FOREIGN KEY (department_id, manager_id) REFERENCES departments(department_id, manager_id)
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Previous: Write a SQL statement to create a table job_history, including employee_id, start_date, end_date, job_id and department_id and make sure that, the employee_id column does not contain any duplicate values at the time of insertion and the foreign key column job_id contain only those values which exist in the jobs table.
Next: Write a sql statement to create a table employees, including columns employee_id, first_name, last_name, email, phone_number hire_date, job_id, salary, commission, manager_id and department_id and make sure that, the employee_id column does not contain any duplicate value at the time of insertion, and the foreign key column department_id, reference by the column department_id of departments table, can contain only those values which exist in the departments table and another foreign key column job_id, referenced by the column job_id of jobs table, can contain only those values which exist in the jobs table.
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