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Relational algebra. In database theory, relational algebra is a theory that uses algebraic structures for modeling data, and defining queries on it with a well founded semantics. The theory was introduced by Edgar F. Codd . The main application of relational algebra is to provide a theoretical foundation for relational databases, particularly ...
Program units are the PL/SQL source code that is developed, compiled, and ultimately executed on the database. PL/SQL anonymous block. The basic unit of a PL/SQL source program is the block, which groups together related declarations and statements. A PL/SQL block is defined by the keywords DECLARE, BEGIN, EXCEPTION, and END.
Apriori [1] is an algorithm for frequent item set mining and association rule learning over relational databases. It proceeds by identifying the frequent individual items in the database and extending them to larger and larger item sets as long as those item sets appear sufficiently often in the database. The frequent item sets determined by ...
Structured type. The SQL:1999 standard introduced a number of object–relational database features into SQL, chiefly among them structured user-defined types, usually called just structured types. These can be defined either in plain SQL with CREATE TYPE but also in Java via SQL/JRT. SQL structured types allow single inheritance .
SQL syntax. The syntax of the SQL programming language is defined and maintained by ISO/IEC SC 32 as part of ISO/IEC 9075. This standard is not freely available. Despite the existence of the standard, SQL code is not completely portable among different database systems without adjustments.
Common Gateway Interface. In computing, Common Gateway Interface ( CGI) is an interface specification that enables web servers to execute an external program to process HTTP or HTTPS user requests. [1] Such programs are often written in a scripting language and are commonly referred to as CGI scripts, but they may include compiled programs. [2]
History. SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd in the early 1970s. This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...
Hash table. A small phone book as a hash table. In computing, a hash table, also known as a hash map or a hash set, is a data structure that implements an associative array, also called a dictionary, which is an abstract data type that maps keys to values. [2] A hash table uses a hash function to compute an index, also called a hash code, into ...
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