Find and fix foreign key violations

To check for a foreign key where the corresponding primary key is missing, run the following command:

Code Sample

  WITH q AS (
      SELECT conrelid::regclass AS fk_table, 
            confrelid::regclass AS pk_table, 
            format('(%s)',(select string_agg(format('fk.%I', attname), ', ') 
                FROM pg_attribute a 
                JOIN unnest(conkey) ia(nr) ON ia.nr = a.attnum
              WHERE attrelid = conrelid)) AS fk_fields, 
            format('(%s)',(select string_agg(format('pk.%I', attname), ', ') 
                FROM pg_attribute a 
                JOIN unnest(confkey) ia(nr) ON ia.nr = a.attnum
              WHERE attrelid = confrelid)) AS pk_fields, 
            pg_get_constraintdef(oid)
        FROM pg_constraint
      WHERE contype='f'
  )
  SELECT format(
  $sql$
  DO $$ BEGIN RAISE NOTICE 'checking Foreign Key %3$s%1$s ==> %4$s%2$s'; END;$$;
  SELECT %1$s, %2$s 
    FROM %3$s AS fk
    LEFT JOIN %4$s AS pk ON %1$s = %2$s 
    WHERE %2$s IS NULL
      AND  %1$s IS NOT NULL  /* any NULL on FK side bypasses FK constraint by design */
  /* use limit for testing, or detecting that "there is a problem in this table */
  --  LIMIT 10
  $sql$, fk_fields, pk_fields, fk_table, pk_table
  )
    FROM q
  \gexec

The output of the script will be similar to the following. If there is no output, there are no violations and you have successfully rebuilt your index.

Output

  id  | pk_id 
  ----+-------
      |     4
  (1 row)

In the above output, the first column shows the primary key columns, in this example, a column named id. The second column is the referencing column for the foreign key. This means there is a row, pk_id=4, for which a parent primary key doesn't exist. You can decide if these keys are valid and if they are not, you can delete them.