What is RDBMS?
RDBMS stands for Relational Database Management System.
RDBMS is a program used to maintain a relational database.
RDBMS is the basis for all modern database systems such as MySQL, Microsoft SQL Server, Oracle, and Microsoft Access.
The data in RDBMS is stored in database objects called tables. A table is a collection of related data entries and it consists of columns and rows.
What is a Database Table?
A table is a collection of related data entries, and it consists of columns and rows.
A column (or field) is a vertical entity in a table, and holds a set of data values of a particular type.
A row (or record) is a horizontal entity in a table, and holds each individual entry in a table.
Look at a selection from the Northwind "Customers" table:
| CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 1 | Alfreds Futterkiste | Maria Anders | Obere Str. 57 | Berlin | 12209 | Germany |
| 2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Avda. de la Constitución 2222 | México D.F. | 05021 | Mexico |
| 3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 05023 | Mexico |
| 4 | Around the Horn | Thomas Hardy | 120 Hanover Sq. | London | WA1 1DP | UK |
| 5 | Berglunds snabbköp | Christina Berglund | Berguvsvägen 8 | Luleå | S-958 22 | Sweden |
The columns in the "Customers" table above are: CustomerID, CustomerName, ContactName, Address, City, PostalCode and Country. The table has 5 records (rows).
What is a Relational Database?
A relational database defines database relationships in the form of tables. The tables are linked to each other - based on data common to each.
Look at a selection of the following three tables: "Customers", "Orders", and "Shippers" from the Northwind database:
Customers Table
| CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 1 | Alfreds Futterkiste | Maria Anders | Obere Str. 57 | Berlin | 12209 | Germany |
| 2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Avda. de la Constitución 2222 | México D.F. | 05021 | Mexico |
| 3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 05023 | Mexico |
| 4 | Around the Horn | Thomas Hardy | 120 Hanover Sq. | London | WA1 1DP | UK |
The relationship between the "Customers" table and the "Orders" table is the CustomerID column:
Orders Table
| OrderID | CustomerID | EmployeeID | OrderDate | ShipperID |
|---|---|---|---|---|
| 10308 | 2 | 7 | 1996-09-18 | 3 |
| 10355 | 4 | 6 | 1996-11-15 | 1 |
| 10365 | 3 | 3 | 1996-11-27 | 2 |
| 10383 | 4 | 8 | 1996-12-16 | 3 |
The relationship between the "Orders" table and the "Shippers" table is the ShipperID column:
Shippers Table
| ShipperID | ShipperName | Phone |
|---|---|---|
| 1 | Speedy Express | (503) 555-9831 |
| 2 | United Package | (503) 555-3199 |
| 3 | Federal Shipping | (503) 555-9931 |
