SQL History and Implementation

In the early 1970's, the seminal work of IBM research fellow Dr. E. F. Codd led to the development of a relational database product called SEQUEL, or Structured English Query Language. SEQUEL due to some legal hurdles was changed to ultimately SQL, or the Structured Query Language. IBM, along with other database vendors, wanted a standardized method for accessing and manipulating data in a relational database. Although IBM was the first to develop relational database theory, Oracle is widely credited with being first to market and popularize the technology. Over time, SQL proved popular … [Read more...]

Introduction to the Relational Model and ANSI SQL

Relational database management systems (RDBMS) such as those covered on this website are the principal engines of structured data systems worldwide. They enable a multitude of users to quickly and simultaneously access, create, edit, and manipulate data without impacting other users. And they enable developers to write useful applications to access their data while providing administrators with the consistent and reliable capabilities they need to maintain, secure, and optimize organizational data resources. An RDBMS may be defined as a system whose users view data as a collection of tables … [Read more...]

Codd’s Rules for Relational Database Systems

E.F. Codd applied rigorous mathematical theories (primarily set theory and relational algebra) to the management of data, and he compiled a list of criteria a database must meet to be considered relational. At its core, the relational database concept centers around storing data in tables. This concept is now so common as to seem trivial; however, not long ago the goal of designing a system capable of sustaining the relational model was considered a long shot with limited usefulness. Following are Codd’s Twelve Principles of Relational Databases: 1.     Information is represented logically … [Read more...]

SQL Statement Classes

Long-standing classes for SQL statements originated back in the days of the SQL92 standard.  These classifications are still common: Data Manipulation Language (DML): SQL statements which manipulate data, such as SELECT, INSERT, UPDATE, DELETE and MERGE. Data Definition Language (DDL): SQL statements control the creation, modification, and removal of database objects, such as CREATE, ALTER and DROP. Data Control Language (DCL): SQL statements related to permissions to execute and access database objects and data, such as GRANT and REVOKE.  Starting with SQL3, seven core categories define the … [Read more...]

What Is a Relational Database?

Relational?!? Move On, Geezer! Maybe you're thinking that relational databases management systems (RDBMSs), like Microsoft SQL Server and Oracle, are going the way of punched cards and rotary phones.  After all, there's been a lot of hype these days in the IT media about the rise of so-called NoSQL (Not Only SQL) databases.  Many new and upcoming CS and MIS graduates who like working with data might think that relational databases are, at best, soon-to-be legacy systems and, at worst, are a career dead-end. Wrong!!! It's true that all the cool-cat computing services (Amazon, Facebook, … [Read more...]