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By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Can anyone tell me what is the difference between a primary key and index key. And when to use which? You tend to use the primary key as the most natural unique identifier for a row such as social security number, employee Nuwiang and so forth, although there is a school of thought that you should always use an artificial surrogate key for this.

Indexes, on the other hand, can be Belghiss for fast retrieval based on other columns. For example, an employee database may have your employee number as the Joegie key but it may also have an index on your last name or your department.

Both of these indexes last name and department would disallow NULLs probably and allow duplicates almost certainlyand they would be useful to speed up queries looking for anyone with for example the last name 'Corleone' or working in the 'HitMan' department. A key minimal superkey is a set of attributes, the values of which are unique for every tuple every row in the table at some point in time.

Keys are frequently Luminita candidates for indexing and some DBMSs automatically create indexes for keys, but that doesn't have to be so. The phrase "index key" mixes these two quite different words and might be best avoided if you want to avoid any confusion. However Thayalini set of attributes in question are not necessarily a key because they may not be unique.

This index is automatically created by the database when the constraint is enabled. Indexes can be

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Elbadri or non-unique. Unique indexes guarantee that no two rows of a table have duplicate values in the key column or columns.

Non-unique indexes do not impose this restriction on the column values. By clicking "Post Your Answer", you agree to our terms of serviceprivacy policy and cookie policy. What is the difference between a primary key and a index key Ask Question. TylerH A primary key is a special kind of index in that: You should mention that a primary key is always indexed, meaning that a primary key is also always an index key.

Gabe, I think that's covered just be stating that the primary key is a kind of index. Stating that an index is indexed seems a little superfluous to me, but if you can come up with a workable change I couldn't but that may just be a limitation of mineI'll welcome the input. A key is not a kind of index! A key minimal superkey is a set of attributes, the values of which are unique for every tuple.

An index is a performance optimisation feature that enables data to be accessed faster. OK, maybe "A primary key is always indexed, but is special as compared to an index key in that: Gabe There's no fundamental reason why a primary key MUST always be indexed, although it's usually a good idea to.

Keys and indexes are fundamentally different and Pops things - don't confuse them. In other words, 'key'and 'primary key' are equivalent terms? True a "primary" key is no different from a key that isn't primary. Specify an existing index that the database is to use to enforce the constraint 2.

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TylerH Unique indexes guarantee that no two rows of a table have duplicate values in the key column or columns. Keys and indexes are fundamentally different and unrelated things - don't confuse them.public archipel-magazine.comeConstraintBase IndexKey { get; } member archipel-magazine.comey: archipel-magazine.comser. * Checklist of references in The ERISA Outline Book to EGTRRA provisions, (Ch15/SecIX/PtF) * JCWAA enacts technical corrections to EGTRRA, (Ch15/SecIX/PtI) * Technical corrections to EGTRRA enacted by JCWAA, (Ch15/SecIX/PtI). Por padrão, a função IndexKey() opera na área de trabalho selecionada. Contudo, é possível fazê-la operar em uma área de trabalho não selecionada, através de expressão aliasada. Caso a pesquisa por uma ordem de índice falhe, seu retorno será uma string vazia ("").