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1. A foreign key value must match an existing value in the parent table or be NULL 2. Foreign keys are based on data values and are purely logical, rather than physical, pointer. CREATE TABLE employees ( employee_id NUMBER(6) , first_name VARCHAR2(20) , last_name VARCHAR2(25) NOT NULL , email VARCHAR2(25) , phone_number VARCHAR2(20) , hire_date DATE ..... ,department_id NUMBER(4) ,CONSTRAINT emp..

1. A foreign key value must match an existing value in the parent table or be NULL 2. Foreign keys are based on data values and are purely logical, rather than physical, pointer. CREATE TABLE employees ( employee_id NUMBER(6) , first_name VARCHAR2(20) , last_name VARCHAR2(25) NOT NULL , email VARCHAR2(25) , phone_number VARCHAR2(20) , hire_date DATE ..... ,department_id NUMBER(4) ,CONSTRAINT emp..

1. Only one primary key can be created for each table.2. Uniquely identifies each row in a table.3. Enforces uniqueness.4. Enforces NOT NULL constraints implicitly.

1. Only one primary key can be created for each table.2. Uniquely identifies each row in a table.3. Enforces uniqueness.4. Enforces NOT NULL constraints implicitly.

1. Either the table level or the column level CREATE TABLE employees ( employee_id NUMBER(6), last_name VARCHAR2(25) NOT NULL, email VARCHAR2(25), ... ... CONSTRAINT emp_email_uk UNIQUE(email)); ** The Oracle server enforces the UNIQUE constaint by implicityly creating a unique index on the unique key column or columns.

1. Either the table level or the column level CREATE TABLE employees ( employee_id NUMBER(6), last_name VARCHAR2(25) NOT NULL, email VARCHAR2(25), ... ... CONSTRAINT emp_email_uk UNIQUE(email)); ** The Oracle server enforces the UNIQUE constaint by implicityly creating a unique index on the unique key column or columns.

Column-level constraint: CREATE TABLE employees( employee_id NUMBER(6) CONSTRAINT emp_emp_id_pk PRIMARY KEY, first_name VARCHAR2(20), ...); Table-level constraint: CREATE TABLE employees( employee_id NUMBER(6), first_name VARCHAR2(20), ... job_id VARCHAR2(10) NOT NULL, CONSTRAINT emp_emp_id_pk PRIMARY_KEY(EMPLOYEE_ID));

Column-level constraint: CREATE TABLE employees( employee_id NUMBER(6) CONSTRAINT emp_emp_id_pk PRIMARY KEY, first_name VARCHAR2(20), ...); Table-level constraint: CREATE TABLE employees( employee_id NUMBER(6), first_name VARCHAR2(20), ... job_id VARCHAR2(10) NOT NULL, CONSTRAINT emp_emp_id_pk PRIMARY_KEY(EMPLOYEE_ID));

- NOT NULL - UNIQUE - PRIMARY KEY - FOREIGN KEY - CHECK You can name a constraint, or the Oracle server automatically generates a name by using the SYS_Cn All constraints are stored in the data dictionary. SYS_Cn n is an integer so that the constraint name is unique. Define a constraint at the column or table level. * Syntax CREATE TABLE [schema.]table (column datatype [DEFAULT expr] [column_con..

- NOT NULL - UNIQUE - PRIMARY KEY - FOREIGN KEY - CHECK You can name a constraint, or the Oracle server automatically generates a name by using the SYS_Cn All constraints are stored in the data dictionary. SYS_Cn n is an integer so that the constraint name is unique. Define a constraint at the column or table level. * Syntax CREATE TABLE [schema.]table (column datatype [DEFAULT expr] [column_con..