In a relational database, all data is contained in tables, which are made up of rows and columns.
Each table has one or more columns, and each column is assigned a specific data type, such as an integer number, a sequence of characters (for text), or a date. Each row in the table has at most one value for each column.Where there is no value for a particular row and column, we sometimes say that the value is NULL, which may be interpreted as not currently known, or not applicable, or not yet available.
An example of a table containing employee information may appear as follows:
emp_ID |
emp_lname |
emp_fname |
emp_phone |
|---|---|---|---|
10057 |
Huong |
Zhang |
1096 |
10693 |
Donaldson |
Anne |
7821 |