What is not a relational operation is

Relational operations include selection, projection, joining, and division.

Set operations are binomial operations and include the four operations of union, difference, intersection, and generalized Cartesian product.

There are two types of basic operations for relations: traditional set operations (merge, difference, intersection, etc.) and specialized relational operations (select, project, join, divide, outer join, etc.) Some queries require a combination of several basic operations that take several steps to complete.

Set operators: merge, difference, intersection, Cartesian product

Specialized relational operators: select, project, join, divide

Traditional set operations

Merge:

Featured are two relations, R and S, which have the same structure.The merge of R and S is the set of tuples belonging either to R or to S. The operator is "U".

Difference:

There are two relations R and S which have the same structure.The difference of R and S is the set consisting of tuples belonging to R but not to S. The operator is "-".

Intersection:

There are two relations R and S, which have the same structure. the intersection of R and S is the set of tuples belonging to R and S. The operator is "n"

Specialized relational operations

Selection:

Selecting tuples from a given relation according to a given set of conditions. tuples to form a new relation, whose relation pattern remains unchanged, but the number of tuples in it is less than or equal to the number of tuples in the original relation, which is a subset of the original relation, with the operator "σ".

Projection:

Selects certain attributes from the specified relationship to form a new relationship, whose relationship schema tends to contain fewer attributes than the original relationship, or the attributes are arranged in a different order. The result of the projection will cancel duplicate tuples created by canceling certain columns, with the operator "π".

Expression: πA(R) = {t[A]|t∈R}

Join:

Splices two and more relational schemas into a relational schema containing more attributes by means of attribute columns in the public ***, the resulting new relation contains tuples that satisfy the conditions for joining, with the operator "∞" , which are categorized as non-equivalent joins, equivalent joins (a special case of conditional joins (or theta joins) when the join operator is the "=" sign, i.e., when theta = 0), and natural joins (where duplicate attributes are removed on top of the equivalent joins).

Division operation:

Let the result of dividing a relation R by a relation S be a relation T. Then T contains all the attributes and values that are in R but not in S, and the tuple of T and the tuple of S are both in R.

★? Relational Operations

A relational operation is a comparison operation in which two objects (constants, variables, expressions, or functions, etc.) are compared to determine whether the result of their comparison satisfies a given condition

★? Relational expressions

The value of a relational expression is a logical value ("true" or "false"), but C doesn't set up logical data; instead, it expresses the logical "true" as However, C does not set up logical data, but instead expresses the logical "true" as the integer constant 1 and the logical "false" as the integer constant 0. If the result of the comparison satisfies the given conditions, then the relational expression satisfies the given conditions. If the result of the comparison satisfies the given condition, the relational expression evaluates to 1. If the result of the comparison does not satisfy the given condition, the relational expression evaluates to 0

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