An identity column assigns a unique value to a database table column, but it’s not inherently unique. It requires a seed and an increment, and can cause data gaps when information is deleted. The administrator must note the numbers already in use to avoid errors.
An identity column is used in database management to add a generated value to a column in a database table. Unless the database administrator plans the identification key, since an identity column is not inherently unique, this could lead to redundant information. Two numbers are needed to create the identity field; one is for the seed, or primary number, and the second is the increment, which goes up with each new piece of information in the column. Using this column in a database where information is frequently deleted could cause data gaps.
When an identity column is added to a database, it identifies that column with a specific set of numbers, set by the administrator or by the database itself. This makes the database column like a column in a spreadsheet, where each cell has its own identity. The main use of the identity function is to assign a unique number to the column, so that the administrator can easily find and call it.
While the identity column is supposed to help make sections of the database unique, by itself it doesn’t. An administrator can assign the same identity numbers to two separate columns and the database will return no errors. Usually, the administrator will only find out when he asks for a table and will receive several in return. To overcome this problem, it is best for the administrator to note the numbers that are already in use.
The identity function takes both a seed and an increment and specifies the first cell in the column. The seed is the first number and serves as the primary identifying aspect of the entire column and the increment is the exact cell number in the column. A database administrator can set the identity column numbers in the function, or the database can automatically assign a value of 1,1 to the column. If your admin sets the column as 3.5, for example, 3 is the seed and 5 is the increment, and the increment will increase with each new cell. This is because the identity function only specifies the first cell and the database takes over from there.
In combination with a database that contains frequently deleted data, an identity column might experience some problems. When data is deleted, the column does not automatically renumber, so the column can jump from 3.5 to 3.8 without the other cells being present. By itself, this usually doesn’t cause problems, but it can make organizing the identity function data more difficult.
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