Unique constraints roll your transaction back. Put your `INSERT` in a nested transaction and you can fall back to `SELECT`, and keep going without throwing away previous work. In multi-table, write-heavy workloads, this insert-or-select path begs for nested transactions so you can lean on uniqueness constraints while keeping your transaction afloat. So far I'm not convinced to abandon that pattern by this article, but I'll keep an eye out for a happier path I guess.