Identity column

An identity column is a <a href="/facts/Column_(database)/WB91xSVs">column</a> (also known as a <a href="/facts/Field_(computer_science)/jt622EDb">field</a>) in a <a href="/facts/Database/VYcpkevb">database</a> <a href="/facts/Table_(database)/5INvK1Vd">table</a> that is made up of values generated by the database. This is much like an <a href="/facts/AutoNumber/SpMf0S1W">AutoNumber</a> field in <a href="/facts/Microsoft_Access/1tID4rKM">Microsoft Access</a> or a sequence in <a href="/facts/Oracle_database/FHv5g732">Oracle</a>. Because the concept is so important in <a href="/facts/Database/VYcpkevb">database</a> <a href="/facts/Science/IJoaD7rs">science</a>, many <a href="/facts/RDBMS/pEKGmJLy">RDBMS</a> systems implement some type of generated key, although each has its own terminology. Today a popular technique for generating identity is to generate a random <a href="/facts/Universally_unique_identifier/SUtkYJPe">UUID</a>. 
An identity column differs from a <a href="/facts/Primary_key/veT9mAbo">primary key</a> in that its values are managed by the server and usually cannot be modified. In many cases an identity column is used as a primary key; however, this is not always the case.
It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to enforce uniqueness on the column you must include the appropriate constraint too.
In <a href="/facts/Microsoft_SQL_Server/eCdt2JBL">Microsoft SQL Server</a> you have options for both the seed (starting value) and the increment. By default the seed and increment are both 1.

Identity column open-in-new

Identity column