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A PL/SQL block is defined by the keywords DECLARE, BEGIN, EXCEPTION, and END. These keywords divide the block into a declarative part, an executable part, and an exception-handling part. The declaration section is optional and may be used to define and initialize constants and variables. If a variable is not initialized then it defaults to NULL ...
What the functions do. The functions are simple data validation and data type checking functions. The data validation functions determine whether it is possible to convert or coerce the data value given as an argument to the function to the type implied by the function name, and return a Boolean value recording whether it was possible or not.
In SQL, null or NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd , SQL null serves to fulfil the requirement that all true relational database management systems ( RDBMS ) support a representation of "missing information and ...
The concept of Null allows SQL to deal with missing information in the relational model. The word NULL is a reserved keyword in SQL, used to identify the Null special marker. Comparisons with Null, for instance equality (=) in WHERE clauses, results in an Unknown truth value.
Database normalization is the process of structuring a relational database in accordance with a series of so-called normal forms in order to reduce data redundancy and improve data integrity. It was first proposed by British computer scientist Edgar F. Codd as part of his relational model. Normalization entails organizing the columns ...
Nullable types are a feature of some programming languages which allow a value to be set to the special value NULL instead of the usual possible values of the data type.In statically typed languages, a nullable type is an option type, [citation needed] while in dynamically typed languages (where values have types, but variables do not), equivalent behavior is provided by having a single null ...
George Boole. In computer science, the Boolean (sometimes shortened to Bool) is a data type that has one of two possible values (usually denoted true and false) which is intended to represent the two truth values of logic and Boolean algebra. It is named after George Boole, who first defined an algebraic system of logic in the mid 19th century.
The null coalescing operator replaces null pointers with a default value. The Haskell equivalent is a way of extracting a value from a Maybe by supplying a default value. This is the function fromMaybe. fromMaybe :: a -> Maybe a -> a fromMaybe defaultValue x = case x of Nothing -> defaultValue Just value -> value.