ENTITY RELATIONSHIP DIAGRAM ENTITY RELATIONSHIP DIAGRAM IS A SPECIALIZED GRAPHIC THAT ILLUSTRATES THE INTERRELATIONSHIPS BETWEEN ENTITIES IN A DATABASE.

SYMBOLS USED IN ENTITY RELATIONSHIP DIAGRAM DIAMOMD ARE NORMALLY USED TO REPRESENT RELATIONSHIPS. OVALS ARE USED TO REPRESENT ATTRIBUTES. BOXES ARE COMMONLY USED TO REPRESENT ENTITIES.

ONE-TO-ONE RELATIONSHIP ONE-TO-ONE RELATIONSHIPS OCCUR WHEN THERE IS EXACTLY ONE RECORD IN THE FIRST TABLE THAT CORRESPONDS TO EXACTLY ONE RECORD IN THE RELATED TABLE. EXAMPLE, This is a one-to-one relationship table design, a STOCK table contains exactly one record in STOCK_DETAIL table. Both tables have the same Stock Id as primary key. In STOCK_DETAIL table, Stock Id is the primary key and also a foreign key to STOCK table.

ONE-TO-MANY RELATIONSHIP ONE -TO-MANY RELATIONSHIPS OCCUR WHEN EACH RECORD IN TABLE A MAY HAVE MANY LINKED RECORDS IN TABLE B BUT EACH RECORD IN TABLE B MAY HAVE ONLY ONE CORRESPONDING RECORD IN TABLE A. EXAMPLE, STUDENT AND PHONE ENTITY. STUDENT CAN HAVE ANY NUMBER OF PHONE NUMBERS. TO CREATE THIS RELATIONSHIP YOU NEED TO HAVE A STUDENT, PHONE AND STUDENT_PHONE TABLE.

MANY-TO-MANY RELATIONSHIP MANY-TO-MANY RELATIONSHIP IS A RELATIONSHIP WHERE MULTIPLE ROWS FROM TABLE A CAN CORRESPOND TO MULTIPLE ROWS IN TABLE B. EXAMPLE, IS A SCHOOL WHERE TEACHERS TEACH STUDENTS. IN MOST SCHOOLS EACH TEACHER CAN TEACH MULTIPLE STUDENTS AND EACH STUDENT CAN BE TAUGHT BY MULTIPLE TEACHERS.