[Koha] .mrc file import issue

[Via Vitae Solutions]

Hi,
  I am new to Koha. I am facing some problem regarding database. If I want
to import a .mrc file after truncating biblio, biblioitems and items
tables, then the biblionumber is increasing. For example, if I truncate
3000 rows from the above tables, then after impoting the .mrc file, it
is starting from 3001.
  If you kindly help why I am not getting biblionumber 1 second time, then
I will be grateful.

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Via Vitae Solutions
Kolkata - 700064
India