An Introduction to SQL and Its Purpose

Structured Query Language is a standard interactive and programming language for getting information from and updating a database.

What is ANSI?

The American National Standards Institute is a private, non-profit organization that administers and coordinates the US voluntary standardization and conformity assessment system.

An example of six commercially use database programs in large companies.

MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase

What is the major difference between Microsoft Access and SQL Server?

The primary difference between the two database programs is in their use. MS Access is primarily used as a local, standalone database on one computer. These databases tend to be smaller and less complex requiring less computing power. SQL Server is a database program which utilizes server and client side installed software. Utilizing the storage and computing capabilities of a server, SQL Server can host complex databases.

The different types of keys and examples of such keys:

Primary Key - a primary key is required attribute in each table and serves as a unique identifier for each row. Example: STU_ID in the STUDENTS table.

Composite Key - Used when more than one attribute is required for functional dependence. Example: STU_NAME and STU_PHONE make up one composite key.

Super Key - a super key is a one or multi-attribute key that functionally determines all of the row's attributes. Example: a super key could be one attribute like STU_ID or multiple - STU_ID and STU_NAME.

Candidate Key - similar to a super key only there are no redundancies in attributes that are already candidate keys. Example: STU_ID and NAME would NOT be a candidate key as STU_ID is a candidate key by itself.

Foreign Key - an attribute that has the same data values of the primary key of another table. Example: STU_ID in the table CLASSES.

Secondary Key - used for data retrieval and is not guaranteed to yield unique results. Example: A student does not know his/her STU_ID so a secondary key is created using STU_NAME and STU_PHONE to retrieve possible unique ids.

Index Key - an ordered arrangement of keys and pointers with each key pointing to the location of the data identified by the key (Rob, Coronel, 89, 2007). Example: Two tables; 1:M; STUDENTS and PAPERS. STU_ID would be the index key to reference the pointers to various papers written by that student.

What are Aliases?

SQL aliases are used to supply alternate names to attributes or tables for display purposes. A user may want column names to display slightly different than their originally assigned name and will create an alias.

These are some of the basics concepts involved in SQL. More detailed examinations can be found in related literature and classes.