relational calculus การใช้

• By Codd's Theorem, this includes relational calculus.
• A view can be defined by an expression using the operators of the relational algebra or the relational calculus.
• The relational model, as expressed through relational calculus and relational algebra, does not distinguish between primary keys and other kinds of keys.
• Originally based upon relational algebra and tuple relational calculus, SQL consists of a data definition language, data manipulation language, and data control language.
• The domain independent relational calculus queries are precisely those relational calculus queries that are invariant under choosing domains of values beyond those appearing in the database itself.
• The domain independent relational calculus queries are precisely those relational calculus queries that are invariant under choosing domains of values beyond those appearing in the database itself.
• Relational calculus is essentially equivalent to first-order logic, and indeed, Codd's Theorem had been known to logicians since the late 1940s.
• The relational algebra and the relational calculus are essentially logically equivalent : for any algebraic expression, there is an equivalent expression in the calculus, and vice versa.
• :The OED notes that " The differential calculus is often spoken of as  the calculus " ( as opposed, for example, to the relational calculus or any other calculus ).
• Codd's Theorem is notable since it establishes the equivalence of two syntactically quite dissimilar languages : relational algebra is a variable-free language, while relational calculus is a logical language with variables and quantification.
• Seminal theoretical work has been accomplished by Libkin et al .; in their model, called NCRA, they extend a nested relational calculus with multidimensional arrays; among the results are important contributions on array query complexity analysis.
• Codd's theorem, a result proven in his seminal work on the relational model, equates the expressive power of relational algebra and relational calculus ( both of which, lacking recursion, are strictly less powerful than first-order logic ).
• Conjunctive queries where all variables are distinguished ( and no variables are bound ) are called "'equi-join queries "', because they are the equivalent, in the relational calculus, of the equi-join queries in the relational algebra ( when selecting all columns of the result ).