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The relational algebra uses set union, set difference, and Cartesian product from set theory, but adds additional constraints to these operators.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.
In information theory, linguistics, and computer science, the Levenshtein distance is a string metric for measuring the difference between two sequences. The Levenshtein distance between two words is the minimum number of single-character edits (insertions, deletions or substitutions) required to change one word into the other.
Set operations (SQL) Set operations in SQL is a type of operations which allow the results of multiple queries to be combined into a single result set. [ 1] Set operators in SQL include UNION, INTERSECT, and EXCEPT, which mathematically correspond to the concepts of union, intersection and set difference .
Hierarchical and recursive queries in SQL. A hierarchical query is a type of SQL query that handles hierarchical model data. They are special cases of more general recursive fixpoint queries, which compute transitive closures. In standard SQL:1999 hierarchical queries are implemented by way of recursive common table expressions (CTEs).
Join (SQL) - Wikipedia. A Venn diagram representing the full join SQL statement between tables A and B. A join clause in the Structured Query Language (SQL) combines columns from one or more tables into a new table. The operation corresponds to a join operation in relational algebra. Informally, a join stitches two tables and puts on the same ...
Select (SQL) The SQL SELECT statement returns a result set of rows, from one or more tables. [1][2] A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used data manipulation language (DML) command. As SQL is a declarative programming language ...
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). Many relational database systems are equipped with the option of using SQL ...
Query language. A query language, also known as data query language or database query language (DQL), is a computer language used to make queries in databases and information systems. In database systems, query languages rely on strict theory to retrieve information. [1] A well known example is the Structured Query Language (SQL).