functional dependency

(database)Given a relation R (in a relational database),attribute Y of R is functionally dependent on attribute X of Rand X of R functionally determines Y of R (in symbols R.X ->R.Y) if and only if each X in R has associated with itprecisely one Y in R (at any one time). Attributes X and Ymay be composite.

This is very close to a function in the mathematical sense.

functional dependency

A dependent relationship between two data elements in a relational database. Used to define normalization, a functional dependency (FD) states that one data element is dependent on another. For example, a social security number (SSN) refers to only one employee (EMP). Expressed as SSN->EMP, employee is dependent on social security number. A product number refers to one product (PRODNO->PRODNAME), and a customer number refers to one customer name (CUSTNO->CUSTNAME). See normalization and transitive dependency.

单词	functional dependency
释义	DictionarySeenormalization functional dependency functional dependency (database)Given a relation R (in a relational database),attribute Y of R is functionally dependent on attribute X of Rand X of R functionally determines Y of R (in symbols R.X ->R.Y) if and only if each X in R has associated with itprecisely one Y in R (at any one time). Attributes X and Ymay be composite. This is very close to a function in the mathematical sense. functional dependency A dependent relationship between two data elements in a relational database. Used to define normalization, a functional dependency (FD) states that one data element is dependent on another. For example, a social security number (SSN) refers to only one employee (EMP). Expressed as SSN->EMP, employee is dependent on social security number. A product number refers to one product (PRODNO->PRODNAME), and a customer number refers to one customer name (CUSTNO->CUSTNAME). See normalization and transitive dependency. AcronymsSeefjord
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