SQL is the abbreviation for structured query language. Its standard form was adopted by the American National Standards Institute and the International Organization for Standardization (ISO) in 1987. The SQL standard is updated every few years and is commonly denoted by ISO/IEC 9075. There are 10 parts to the SQL standard. Those parts are followed by a colon and indicate the latest version. The most important elements of the SQL language are described below.
The SQL language is a standard query language for accessing database information. The full name of the language is Structured Query Language, and it first came into use in the 1970s. IBM created it for government projects. It has become a standard for database access and management. Its original name was SEQUEL, but people pronounce each letter separately. Most people pronounce SQL as S-Q-L, and it is now used worldwide as the standard for database programming.
SQL is based on relational algebra and tuple relational calculus, and includes many types of statements. These statements can be further broken down into sublanguages. The first language, data query language, has three primary categories: data definition, data control, and data manipulation. In general, SQL is a declarative language, but it also has procedural elements. This article explains the basic language of SQL.
SQL has extensions in different database systems. PL/SQL stands for Procedural Language/Structured Query Language, which is used by Oracle. The second type, T-SQL, stands for Transact-SQL, and works on Microsoft SQL Server and Sybase SQL server. These are extensions of the SQL language that allow for the use of advanced features. The following table describes some of the extensions of SQL.
A primary key is a value that is unique to each row in a table. Another important part of a primary key is the uniqueness of the values. A primary key can never have a null value. A secondary key, on the other hand, can be a different value. Using a primary key constraint in a database can help you ensure the integrity of an entity. This is also known as an index.
SQL implementations vary in their semantics and syntax. Some implementations have inconsistent date and time syntax, and other features such as comparison case sensitivity and string concatenation vary among vendors. However, PostgreSQL is a good example of standards compliance, and it folds unquoted names into lower or upper case. If you’re wondering what SQL is, start by learning the history of the language and learn about how it’s used today.