candidate key - определение. Что такое candidate key
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Что (кто) такое candidate key - определение

Prime attribute; Non-prime attribute
Найдено результатов: 1145
candidate key         
<database> One of several possible attributes or combinations of attributes which can be used to uniquely identify a body of information (a "record"). The chosen candidate key is called the primary key. (2006-05-29)
Candidate key         
A candidate key, or simply a key, of a relational database is a minimal superkey. In other words, it is any set of columns that have a unique combination of values in each row (which makes it a superkey), with the additional constraint that removing any column would possibly produce duplicate rows (which makes it a minimal superkey).
Key (music)         
  • ii-V<sup>7</sup>-I progression]] in C [[File:Ii-V-I turnaround in C.mid]]
TONIC NOTE AND CHORD OF A MUSICAL PIECE
Major key; Key (Music); Musical key; Major Key; Key of D; Musical keys; Key coloration; Key relationship; Musical Key; Music key; Minor-key; Minor–key; Major-key; Key of E
In music theory, the key of a piece is the group of pitches, or scale, that forms the basis of a musical composition in classical, Western art, and Western pop music.
Key (cryptography)         
PIECE OF INFORMATION IN CRYPTOGRAPHY
Cryptography/Key; Secret key; Encryption key; Cryptographic keys; Cryptographic key; Key (cryptology); Cryptovariable; Cryptovariables
A key in cryptography is a piece of information, usually a string of numbers or letters that are stored in a file, which, when processed through a cryptographic algorithm, can encode or decode cryptographic data. Based on the used method, the key can be different sizes and varieties, but in all cases, the strength of the encryption relies on the security of the key being maintained.
Natural key         
TYPE OF UNIQUE KEY IN A DATABASE FORMED OF ATTRIBUTES THAT EXIST AND ARE USED IN THE EXTERNAL WORLD OUTSIDE THE DATABASE
Domain key; Business key
A natural key (also known as business keyData modelling: What exactly is a Business Key? by Roy, Rajiv Max.
meta key         
COMPUTER KEY
Diamond key; Metakey; Meta Key
¦ noun Computing a key which activates a function when held down simultaneously with another key.
Product key         
  • Product key on a Proof of License Certificate of Authenticity for [[Windows Vista]] Home Premium
SPECIFIC SOFTWARE-BASED KEY FOR A COMPUTER PROGRAM
Product token; Product tokens; Serial key; Cd-key; Cd key; CD-key; Activation code; License key; Software license key; Software licence key; Software licensing key; Licence key; CD key; CD Key; Product Key; Software key; Game key; Video game key; Registration key
A product key, also known as a software key, serial key or activation key, is a specific software-based key for a computer program. It certifies that the copy of the program is original.
Key (character)         
FICTIONAL SUPERVILLAIN IN DC COMICS
The Key (comics); Key (comics)
Key is the name of a supervillain in the DC Comics universe, a long-time and highly dangerous opponent of the Justice League. The character continues to appear in Justice League and Batman comics, with a ghoulish (rather than human) appearance since 1997.
function key         
  • [[Flexowriter]] keyboard (1968) with 13 function keys on the right
  • [[HP 9830A]] (1972) with 5×2 grid of 10 function keys at top left
KEY ON A COMPUTER OR TERMINAL KEYBOARD
Function Keys; F keys; F1 key; Fkey; Function keys; Function key 1; F2 Key; F3 Key; F4 Key; F5 Key; F6 Key; F1 button; PF keys; F7 key; F8 key; F9 key; F10 key; F11 key; F12 key; FKEYS
<hardware> (From the IBM 3270 terminal's Programmed Function Keys (PF keys)) One of a set of special keys on a computer or terminal keyboard which can be programmed so as to cause an application program to perform certain actions. Function keys on a terminal may either generate short fixed sequences of characters, often beginning with the escape character (ASCII 27), or the characters they generate may be configured by sending special character sequences to the terminal. On a microcomputer keyboard, the function keys may generate a fixed, single byte code, outside the normal ASCII range, which is translated into some other configurable sequence by the keyboard device driver or interpreted directly by the application program. (1995-02-07)
function key         
  • [[Flexowriter]] keyboard (1968) with 13 function keys on the right
  • [[HP 9830A]] (1972) with 5×2 grid of 10 function keys at top left
KEY ON A COMPUTER OR TERMINAL KEYBOARD
Function Keys; F keys; F1 key; Fkey; Function keys; Function key 1; F2 Key; F3 Key; F4 Key; F5 Key; F6 Key; F1 button; PF keys; F7 key; F8 key; F9 key; F10 key; F11 key; F12 key; FKEYS
¦ noun Computing a key on a computer keyboard to which software can assign a particular function.

Википедия

Candidate key

A candidate key, or simply a key, of a relational database is a minimal superkey. In other words, it is any set of columns that have a unique combination of values in each row (which makes it a superkey), with the additional constraint that removing any column could produce duplicate combinations of values (which makes it a minimal superkey). Because a candidate key is a superkey that doesn't contain a smaller one, a relation can have multiple candidate keys, each with a different number of attributes.

Specific candidate keys are sometimes called primary keys, secondary keys or alternate keys.

The columns in a candidate key are called prime attributes, and a column that does not occur in any candidate key is called a non-prime attribute.

Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that isn't minimal, some subset of that will be minimal.

There is a functional dependency from the candidate key to all the attributes in the relation.

The superkeys of a relation are all the possible ways we can identify a row. The candidate keys are the minimal subsets of each superkey and as such, they are an important concept for the design of database schema.