Native SQL is counted among the so-called declarative languages (4GL fourth generation languages), result-oriented. In languages of this type of user defines what the end result is to achieve as a result of the selected command without specifying how this should be done.
The "how" to get an SQL command determines Database Management System, which, after receiving instructions to execute performs activities related to its implementation (syntax analysis, optimization, development plan, execute the command and execution of the prepared plan).
SQL commands do not include the implementation of the program control statements, such as conditional statements and looping structures, because the user does not need to specify how to perform a command. The logic of action in the context of the SQL database is based on the algebra of relations, which operates on the data sets.
A characteristic feature is the use of three-valued logic, ie one in which outside the boolean values true (true) and false (false) is also found value unknown (unknown), represented by null.
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