Question

What could possibly caused a FK error? I’m inserting an ‘Activity’ record into a database that has a ‘StaffId’ field on (FK with Staff table), I’ve looked for the staffId in question (no white spaces etc.) and it DOES exist. What else can cause an error with a foreign key field?

EDIT: Error:

The INSERT statement conflicted with the FOREIGN KEY constraint
“FK_Activities_Staff”. The conflict occurred in database
“DataWarehouseB”, table “dbo.Staff”, column ‘StaffId’. The statement
has been terminated.

Answer 1

SQL Foreign Key documentation says

If the database schema contains foreign key errors that require
looking at more than one table definition to identify, then those
errors are not detected when the tables are created. Instead, such
errors prevent the application from preparing SQL statements that
modify the content of the child or parent tables in ways that use the
foreign keys. Errors reported when content is changed are “DML errors”
and errors reported when the schema is changed are “DDL errors”. So,
in other words, misconfigured foreign key constraints that require
looking at both the child and parent are DML errors. The English
language error message for foreign key DML errors is usually “foreign
key mismatch” but can also be “no such table” if the parent table does
not exist. Foreign key DML errors are may be reported if:

• The parent table does not exist.
• The parent key columns named in the foreign key constraint do not exist.
• The parent key columns named in the foreign key constraint are not the primary key of the parent table and are not subject to a
  unique constraint using collating sequence specified in the CREATE
  TABLE.
• The child table references the primary key of the parent without specifying the primary key columns and the number of primary key
  columns in the parent do not match the number of child key columns.

Some DBs might also support using a non-unique index as a foreign key reference,