The first time you insert a row into the table, an IDENTITY column has a value of 1 assigned to it. On each subsequent insert, the value of the column increases by one. The value most recently inserted into an identity column is available in the @@identity global variable.
The value of @@identity changes each time a statement attempts to insert a row into a table.
If the statement affects a table without an IDENTITY column, @@identity is set to 0.
If the statement inserts multiple rows, @@identity reflects the last value inserted into the IDENTITY column.
This change is permanent. @@identity does not revert to its previous value if the statement fails or if the transaction that contains it is rolled back.
For more information on the behavior of @@identity, see @@identity global variable.