sql: CockroachDB accepts invalid characters in identifiers

[knz]

Currently CockroachDB accepts nul and newline characters in double-quoted identifiers. It also accepts invalid UTF-8 sequences inside single-quoted identifiers.

This makes pretty-printed queries hard to read and arguably would confuse UI clients that try to display the name of the database objects.

pg's docs specify that SQL identifiers and key words must begin with a letter (a-z, but also letters with diacritical marks and non-Latin letters) or an underscore (_). Subsequent characters in an identifier or key word can be letters, underscores, digits (0-9), or dollar signs ($).

https://www.postgresql.org/docs/10/static/sql-syntax-lexical.html

It's probably OK if CockroachDB supports slightly more (valid UTF-8 strings, for example) but we should reject at least control characters.

Jira issue: CRDB-4999

[github-actions]

We have marked this issue as stale because it has been inactive for
18 months. If this issue is still relevant, removing the stale label
or adding a comment will keep it active. Otherwise, we'll close it in
5 days to keep the issue queue tidy. Thank you for your contribution
to CockroachDB!

[knz]

This issue is still current as of 21.1