Introduction to SQL
What is SQL?
- SQL stands for Structured Query Language.
- SQL allows you to access a database.
- SQL is an ANSI standard computer language.
- SQL can execute queries against a database.
- SQL can retrieve data from a database.
- SQL can insert new records in a database.
- SQL can delete records from a database.
- SQL can update records in a database.
SQL is a Standard—BUT....
SQL is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating database systems.
SQL statements are used to retrieve and update data in a database.
SQL works with database programs like Access, DB2, Informix, SQL Server, Oracle, Sybase, etc.
Unfortunately, there are many different versions of the SQL language, but to be in compliance with the ANSI standard, they must support the same major keywords in a similar manner (such as SELECT, UPDATE, DELETE, INSERT, WHERE, and others).
SQL Database Tables
A database most often contains one or more tables.
Each table is identified by a name (e.g., “Customers” or “Orders”).
Tables contain records (rows) with data.
Below is an example of a table called Persons:
| LastName
|
FirstName
|
Address
|
City
|
| Hansen |
Ola |
Timoteivn 10 |
Sandnes |
| Svendson |
Tove |
Borgvn 23 |
Sandnes |
| Pettersen |
Kari |
Storgt 20 |
Stavanger |
The table above contains three records (one for each person) and four columns (LastName, FirstName, Address, and City).