Allows foreign key to be deferred during a transaction, but it will be applied immediately if not deferred.

PostgreSQL_deferrable_foreign_key.sql

ALTER TABLE "TableName"
ADD CONSTRAINT "ConstraintName" FOREIGN KEY ("columnName")
  REFERENCES "AnotherTableName" ("anotherColumnName") MATCH SIMPLE
  ON UPDATE CASCADE ON DELETE CASCADE DEFERRABLE INITIALLY IMMEDIATE;

-- I generally use the form "TableName_fk_constraintname" for foreign key constraint names (for reference)
-- This particular foreign key will cascade on update and delete, but those particular directives aren't required. (for reference)