Many databases start in a word processing program or spreadsheet, but as they get larger many businesses will find it helpful to transfer them to a database created by a database management system.
In order to control the information in those databases, SQL is used, which allows users to retrieve the specific data they are looking for when they need it. While it is a simple programming language, SQL is also very powerful. The website Database Dir says SQL can insert data into database tables, modify data in existing database tables and delete data from SQL database tables. In addition, SQL can modify the database structure itself by creating, modifying and deleting tables and other database objects.
With so many companies now relying on big data analytics to drive their direction, employees with SQL skills and backgrounds are some of the most sought after by employers. In his paper, Todd proposed that that all data in a database be represented in the form of relations. It wasn't until several years later, however, that the SQL language was made available publicly.
Rather than trying to write an SQL for their own databases, many companies use a database management system that has SQL already built in to it. The software is an open source version, which means it can be downloaded and used for free. According to the web hosting service GoDaddy, MySQL is a sophisticated and powerful relational database used by many websites to create and change content quickly.
Websites that use dynamic Web pages are often referred to as database-driven websites. Great decision! Either way, it's worth knowing the history of SQL — where it came from, who came up with it, and why.
The first computer databases appeared in the late s. This was an important area of research at the time. Many computer scientists were focused on improving how databases work. But what Codd is really famous for is an article published in called A Relational Model of Data for Large Shared Data Banks ; this started the era of relational databases in computer science. Codd is therefore often referred to as the forefather of SQL. At the time Codd wrote his article, hierarchical and network databases were dominant.
They were also quite inflexible. To get data out of the database, you essentially had to write a computer program: the data were not accessible to non-programmers. Any change in the model required changes in data access patterns — in other words, the data access programs basically had to be rewritten. In his article, Codd proposed a completely new idea: modeling data with the mathematical notion of relations.
Today, we call them tables. New relations could be added without modifying existing relations. Thanks to his ideas, working with databases has become much easier. IBM was not eager to implement his suggestions. At the time, they had IMS , a very successful hierarchical database. They didn't want to undermine their revenue from IMS by building a competing product. IMS is still developed today, which shows how successful it was. Two people involved in System R development, Don Chamberlin and Ray Boyce, were in charge of creating its query language.
In his seminal article, Codd proposed a set of operations that could be used to extract data from relations. You can think of these operations as the first query language for relational databases. After you have completed the task, examine the results, and then reset the job code to its original value.
Assuming that the data shown in the Employee table have been entered, write the SQL code that lists all attributes for a job code of Write the SQL code to delete the row for the person named William Smithfield, who was hired on June 22, , and whose job code classification is Hint : Use logical operators to include all the information given in this problem.
You may assume that the table will be restored to its original condition preceding this question. Date, C. Relational Database Selected Writings. Skip to content Main Body. Figure Employee table with data for questions , by A. Previous: Chapter 14 Database Users.
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