The best replacement for primary key is foreign key.

The best alternatives to primary key are rated as following:
★★★★★  foreign key
★★★★  unique key
★★★★  unique index
★★  index
★★  unique constraint
★★  clustered index
★★  candidate key
★  unique
★  identity
★  key
★  surrogate key
★  primary index
★  composite key
★  super key
  natural key
  unique clustered index
  unique key sql
  unique not null
  unique identifier
  identifier
  key mysql
  unique constraints

Your alternative for primary key is not listed? Suggest!
Speaking about primary key, one probably shouldn't forget about index.

Other search terms related to primary key and their ratings are:
★★★★★ index
★★★ auto increment
★★★ duplicates
★★ auto increment in mysql
★★ auto increment mysql
★★ example in sql
★★ clustered
★ auto_increment in mysql
★ non clustered index
★ unique index
★ more than one field
★ clustered index
more than one column
alter table
mysql
You have in mind a companion for primary key and it is not yet here? Propose!



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primary key
foreign key
unique key