SQL Overview

1. SQL Overview Structured Query Language

2. Description • When Codd first described the theory of relational databases, he asserted that there should be a comprehensive language that would describe both the data and the meta data. • SQL has developed into that language

3. SQL Features • SQL does not come as a separate package • It is always a part of a Data Base Management system • SQL is a fourth generation language (meaning it is not procedural. You describe what you want to do not how to do it)

4. Standards • SQL is an ANSI standard • Most DBMS implement the 1992 standard, some are beginning to implement the 1999 standard • In addition to the standard SQL most DBMSs add their own commands and features • SQL Server has T-SQL • Oracle has PSQL

5. Three Uses • To define data (including setting indexes and user permissions) • To query data • To manipulate data

6. Data Definition • You can define all the data structures in a relational database with SQL CREATE TABLE tblCustomer ( CustomerID Integer Primary Key, CustomerLastName varchar(50), CustomerFirstName varchar(35) )

7. Data Query • You can retrieve any data or combination of the data from the database with SQL queries SELECT CustomerLastName, CustomerFirstname, OrderID, OrderDate FROM tblCustomer c INNER JOIN tblOrder o ON c.CustomerID=o.CustomerID WHERE c.CustomerID=5;

8. Data Manipulation • You can Insert, Update and Manipulate data with SQL UPDATE tblCustomer SET LastName=‘Smith’ WHERE CustomerID=7;