What is the difference between primary key and index in oracle

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Learn how your comment data is processed. The opinions expressed here represent my own and not those of my employer. My employer do not endorse any tools, applications, books, or concepts mentioned on the blog. I have documented my personal experience on this blog. Email Address:. The primary key does not accept the any duplicate and NULL values. The primary key value in a table changes very rarely so it is chosen with care where the changes can occur in a seldom manner.

A primary key of one table can be referenced by foreign key of another table. Attention reader! Skip to content. Change Language. Indexes, on the other hand, can be used for fast retrieval based on other columns. For example, an employee database may have your employee number as the primary 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 certainly , and 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 good 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 the 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 unique 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.

A Primary Index is your table's data structure, but only if your data structure is ordered by the Primary Key, thus allowing efficient lookups without a requiring a separate data structure to look up records by the Primary Key. Not all databases have a Primary Index. Most of those that don't build a secondary index on the Primary Key by default. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Newsletters may contain advertising.

You can unsubscribe at any time. I would like to know the difference between primary key and primary index. Can anyone help me out. U nead to refer to teradata doc to know more about it. No Account?