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The referenced column(s) in the referenced table must be under a unique constraint, such as a primary key. Also, self-references are possible (not fully implemented in MS SQL Server though [5]). On inserting a new row into the referencing table, the relational database management system (RDBMS) checks if the entered key value exists in the ...
Key Code Qualifier is an error-code returned by a SCSI device. When a SCSI target device returns a check condition in response to a command , the initiator usually then issues a SCSI Request Sense command .
Names must not be purely numeric; the software will accept something like ":31337" (which is punctuation plus a number), but it will ignore "31337" (purely numeric). Names should have semantic value, so that they can be more easily distinguished from each other by human editors who are looking at the wikitext.
In a relational database, a candidate key uniquely identifies each row of data values in a database table. A candidate key comprises a single column or a set of columns in a single database table. No two distinct rows or data records in a database table can have the same data value (or combination of data values) in those candidate key columns ...
KEY: 25: RFC 2535 [3] and RFC 2930 [4] Key record: Used only for SIG(0) (RFC 2931) and TKEY (RFC 2930). [5] RFC 3445 eliminated their use for application keys and limited their use to DNSSEC. [6] RFC 3755 designates DNSKEY as the replacement within DNSSEC. [7] RFC 4025 designates IPSECKEY as the replacement for use with IPsec. [8]
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
A candidate key, or simply a key, of a relational database is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column could produce duplicate combinations of values. A candidate key is a minimal superkey, [1] i.e., a superkey that does not contain a smaller one. Therefore ...
In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...