sql-serversql-server-2005t-sqltruncateforeign-keys

Cannot truncate table because it is being referenced by a FOREIGN KEY constraint?


Using MSSQL2005, can I truncate a table with a foreign key constraint if I first truncate the child table (the table with the primary key of the FK relationship)?

I know that I can either

  • Use a DELETE without a where clause and then RESEED the identity (or)
  • Remove the FK, truncate the table, and recreate the FK.

I thought that as long as I truncated the child table before the parent, I'd be okay without doing either of the options above, but I'm getting this error:

Cannot truncate table 'TableName' because it is being referenced by a FOREIGN KEY constraint.


Solution

  • Correct; you cannot truncate a table which has an FK constraint on it.

    Typically my process for this is:

    1. Drop the constraints
    2. Trunc the table
    3. Recreate the constraints.

    (All in a transaction, of course.)

    Of course, this only applies if the child has already been truncated. Otherwise I go a different route, dependent entirely on what my data looks like. (Too many variables to get into here.)

    The original poster determined WHY this is the case; see this answer for more details.