My SQL

• Sophia Fraser, "My SQL"
• Global Media | 2009 | ISBN: 9380168446 | 72 pages | PDF | 1 MB
• Introduction
• Relational Databases
• The main drive behind a relational database
• is to increase accuracy by increasing the
• efficiency with which data is stored. For example, the names of each of the millions of
• people who immigrated to the United States through Ellis Island at the turn of the 20th
• century were recorded by hand on large sheets of paper; people from the city of London
• had their country of origin entered as England, or Great Britain, or United Kingdom, or
• U.K., or UK, or Engl., etc. Multiple ways of recording
• the same information leads to
• future confusion when there is a need to simply know how many people came from the
• country now known as the United Kingdom.
• The modern solution to this problem is the database. A single entry is made for each
• country, for example, in a reference list that might be called the Country table. When
• someone needs to indicate the United Kingdom, he only has one choice available to him
• from the list: a single entry called "United Kingdom". In this example, "United Kingdom"
• is the unique representation of a country, and any further information about this country
• can use the same term from the same list to refer to the same country. For example, a list
• of telephone country codes and a list of European castles both need to refer to countries;
• by using the same Country table to provide this identical information to both of the new
• lists, we've established new relationships among different lists that only have one item in
• common: country. A relational database, therefore, is simply a collection of lists that
• share some common pieces of information.
• If you are not familiar with the concepts of databases, you can begin with Database
• Programming.
• Structured Query Language (SQL)
• SQL, which is initialism for Structured Query Language, is a language to request data
• from a database, to add, update, or remove data within a database, or to manipulate the
• metadata of the database.
• SQL is generally pronounced as the three letters in the name, e.g. ess-cue-ell, or in some
• people's usage, as the word sequel.
• SQL is a declarative language in which the expected result or operation is given without
• the specific details about how to accomplish the task. The steps required to execute SQL
• commands are handled transparently by the SQL database
• . Sometimes SQL is
• characterized as non-procedural because procedural languages generally require the
• details of the operations to be specified, such as opening and closing tables, loading and
• searching indexes, or flushing buffers and writing data to filesystems. Therefore, SQL is
• considered to be designed at a higher conceptual level of operation than procedural>
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