title: Simple constraint to limit an Oracle table to a single row
body: <p>I'm looking for a simple way to limit an application configuration table to 1 row.  I know I can do this with a virtual column containing a subquery, or a materialized view on top, but really it's a simple table I'd like a constraint that doesn't take more lines to implement than to create the table.</p>
  
  <p>Simplest way I've thought of is an ID field set to 1, and a check constraint that the ID has to be 1 - but this adds a confusing extra field to the table so I'm hoping there's something obvious I'm missing, like a check constraint where UNIQUE_FIELD = MAX(UNIQUE_FIELD), which is not allowed.</p>