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  2. Relational model - Wikipedia

    en.wikipedia.org/wiki/Relational_model

    Most relational databases use the SQL data definition and query language; these systems implement what can be regarded as an engineering approximation to the relational model. A table in a SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries ...

  3. Query by Example - Wikipedia

    en.wikipedia.org/wiki/Query_by_Example

    Query by Example (QBE) is a database query language for relational databases. It was devised by Moshé M. Zloof at IBM Research during the mid-1970s, in parallel to the development of SQL . [ 1 ] It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions.

  4. Database theory - Wikipedia

    en.wikipedia.org/wiki/Database_theory

    Database theory encapsulates a broad range of topics related to the study and research of the theoretical realm of databases and database management systems.. Theoretical aspects of data management include, among other areas, the foundations of query languages, computational complexity and expressive power of queries, finite model theory, database design theory, dependency theory, foundations ...

  5. Relational database - Wikipedia

    en.wikipedia.org/wiki/Relational_database

    A relational database (RDB [1]) is a database based on the relational model of data, as proposed by E. F. Codd in 1970. [ 2 ] A database management system used to maintain relational databases is a relational database management system ( RDBMS ).

  6. Query optimization - Wikipedia

    en.wikipedia.org/wiki/Query_optimization

    A SQL query to a modern relational DBMS does more than just selections and joins. In particular, SQL queries often nest several layers of SPJ blocks (Select-Project-Join), by means of group by, exists, and not exists operators. In some cases such nested SQL queries can be flattened into a select-project-join query, but not always. Query plans ...

  7. Database model - Wikipedia

    en.wikipedia.org/wiki/Database_model

    The basic data structure of the relational model is the table, where information about a particular entity (say, an employee) is represented in rows (also called tuples) and columns. Thus, the "relation" in "relational database" refers to the various tables in the database; a relation is a set of tuples. The columns enumerate the various ...

  8. Database normalization - Wikipedia

    en.wikipedia.org/wiki/Database_normalization

    The Relational Model for Database Management: Version 2: California: 1 The Relational Model for Database Management: Version 2 Texas 1: Learning SQL: Texas: 1: Beginning MySQL Database Design and Optimization: Texas: 2 The Relational Model for Database Management: Version 2 California

  9. Database server - Wikipedia

    en.wikipedia.org/wiki/Database_server

    Every server uses its own query logic and structure. The SQL (Structured Query Language) query language is more or less the same on all relational database applications. For clarification, a database server is simply a server that maintains services related to clients via database applications. DB-Engines lists over 300 DBMSs in its ranking. [3]