2017-01-24 19:15 GMT+01:00 David G. Johnston <david.g.johnston@gmail.com>: > > Then consider a feature request that a malformed pattern be detected and fail independent of the data being checked. Such non-deterministic failure is at least a POLA violation and makes what should be a basically compile-time error into a run-time one.
This is not pure compile-time "error" as pattern in LIKE could be dynamic expression, for example:
But now we're no longer talking about an expression of the form "LIKE constant". In SQL whenever you decide to write a query that involves tables and columns you run the risk of introducing run-time bugs if you make assumptions about the contents of those columns that fail to hold. So if you decide to write queries of that form you should define table t like so:
create table t (a varchar check (a !~ '\$')) -- which could be improved upon depending on your needs - but it would at least catch every actual invalid expression at the cost of disallowing valid ones.
