This article outlines the database structure for the MMv4 tax_zone database table.

• id
  Primary Key of the table.
  int(10) | unsigned | auto increment | primary key | indexed
  
• object_id
  A reference to the tax.id field that this tax_zone is associated with.
  int(10) | unsigned | indexed
• zone_type
  The type of zone this tax will be applied to. Z = zip code, S = state and C = country.
  char(1) | values: Z,S,C | default: Z | indexed
  
• zone
  The zip code or ISO code of the state/country the tax will be applied to.
  varchar(255) | indexed