Solutions for INSERT OR UPDATE on SQL Server

Question

Assume a table structure of MyTable(KEY, datafield1, datafield2...).

Often I want to either update an existing record, or insert a new record if it does

Answer 1

Before everyone jumps to HOLDLOCK-s out of fear from these nafarious users running your sprocs directly :-) let me point out that you have to guarantee uniqueness of new PK-s by design (identity keys, sequence generators in Oracle, unique indexes for external ID-s, queries covered by indexes). That's the alpha and omega of the issue. If you don't have that, no HOLDLOCK-s of the universe are going to save you and if you do have that then you don't need anything beyond UPDLOCK on the first select (or to use update first).

Sprocs normally run under very controlled conditions and with the assumption of a trusted caller (mid tier). Meaning that if a simple upsert pattern (update+insert or merge) ever sees duplicate PK that means a bug in your mid-tier or table design and it's good that SQL will yell a fault in such case and reject the record. Placing a HOLDLOCK in this case equals eating exceptions and taking in potentially faulty data, besides reducing your perf.

Having said that, Using MERGE, or UPDATE then INSERT is easier on your server and less error prone since you don't have to remember to add (UPDLOCK) to first select. Also, if you are doing inserts/updates in small batches you need to know your data in order to decide whether a transaction is appropriate or not. It it's just a collection of unrelated records then additional "enveloping" transaction will be detrimental.