Sometime primary keys are obvious, for example a car license plate could be used to uniquely identify cars. Often, primary keys are less obvious and it is necessary to create a unique value ...

In this example, Transact-SQL will create a new table with all columns from the rows in "old_table" in which the last name starts with "Ja." ...

Foreign key 'geneassay_fk' references invalid column 'geneassay' in referencing table 'b_SequencingData_seq'. Msg 1750, Level 16, State 0, Line 43 Could not create constraint.

It's best practice to declare the foreign keys according to functional dependencies. E.g. if your other table is about salespeople, then its foreign key should refer to Salespeople.