SQL is a set-oriented programming language that is designed to allow people to query and update tables of information.
All information is stored in tables. A table is divided into rows and columns. (SQL theorists refer to columns as “attributes” and rows as “tuples”, but we will use the more familiar terms “columns” and “rows”. We will also use the terms “record” and “row” interchangeably.) Each database contains 0 or more tables. Most databases contain many tables. An example of a table is shown below.
ID
NAME
ADDRESS
1
Beethoven
23 Ludwig Lane
2
Dylan
46 Robert Road
3
Nelson
79 Willie Way
This table contains three rows of data. (The top “row”, which has the labels “ID”, “NAME”, and “ADDRESS” is shown here for the convenience of the reader. The actual table in the database does not have such a row.) The table contains three columns (ID, NAME, and ADDRESS). SQL provides commands to create tables, insert rows into tables, update data in tables, delete rows from tables, and query the rows in tables.