An Entity Relationship Diagram (ERD) is a visual representation of different entities within a system and how they relate to each other.
Agenda: To create ER diagrams for the tables in the database.
Consider a hypothetical scenario in which Restaurant data is stored in a database. The database contains the following tables:
Following are the tables: Food_Item, List_Recipies, Food_Menu, Order_Details, My_Customers, My_Promo, My_Orders, My_Employees, My_Promo
In the diagrams above the Column names in orange are called ‘Entities’ and the keys in green are called ‘Attributes’. The following diagram describes this further.
STEP 1:
Go to phpMyAdmin and create a database named ‘Restaurant’.
STEP 2:
To populate the tables in the database run the following SQL commands.
CREATE TABLE IF NOT EXISTS Food_Item ( id INTEGER NOT NULL PRIMARY KEY , menu_id INTEGER , item_name VARCHAR(40) , Item_price VARCHAR(20) , Stock VARCHAR(20))
CREATE TABLE IF NOT EXISTS Customer( id INTEGER NOT NULL PRIMARY KEY , food_item_id INTEGER , name VARCHAR(40) , contact INTEGER(30) , member_id VARCHAR(20))
CREATE TABLE IF NOT EXISTS Employees( emp_id INTEGER NOT NULL PRIMARY KEY , customer_id VARCHAR(30) , name VARCHAR(40) , address Varchar(20) , salary VARCHAR(20))
CREATE TABLE IF NOT EXISTS Promo( id INTEGER NOT NULL PRIMARY KEY , order_id VARCHAR(30), promo_desc VARCHAR(40) , discount VARCHAR (20) , expiry_date VARCHAR(20))
CREATE TABLE IF NOT EXISTS Food_Menu( id INTEGER NOT NULL PRIMARY KEY, employee_id VARCHAR(20), menu_name VARCHAR(40), price Varchar(20), cooking_time VARCHAR(20))
CREATE TABLE IF NOT EXISTS Orders( id INTEGER NOT NULL PRIMARY KEY , employee_id INTEGER , order_date VARCHAR(40) , order_type Varchar(20) , total_amount VARCHAR(20))
Now your database is populated with all the tables.
Note: You do not need to insert data in the tables to create an Entity Relationship Diagram. You just need the field names and their data types.
STEP 3:
In the top menu select More → Designer option as shown in the image below.
This will open the designing mode. You can see all the tables scattered on the designing sheet something like this:
Now you have to create relationships between the different tables. The following chart will help you to understand the relationships between the two tables better.
STEP 4:
Now create relationships by clicking on the relationship icon on the left menu bar. Then select the primary key and foreign key in a relation and click on create relationship option. Perform the same for all the rest of the tables.
The result will look something like this:
Now you had create ER Diagrams for your database.
STEP 5:
The last page of the report will be as shown below:
Hence these are the basic steps of creating an Entity-Relationship (ER) Diagrams [create ER diagrams] for a database.
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