Column `DEFAULT` only accepts integer literals

[aciddust]

expr is still the stub at src/pegjs/oracle.pegjs#L2711:

// TODO:
expr = integer

column_default_clause (L2067) is the only thing standing between it and a
column definition, so a default parses only when it is a signed whole number.
Everything else fails, including the very common default 'N'.

const { Parser } = require('oracle-sql-parser');
const parser = new Parser();

const t = (d) => {
  try { parser.parse(`create table t (a varchar2(10) ${d});`); console.log('OK  ', d); }
  catch (e) { console.log('FAIL', d, '->', e.message); }
};

t("default 0");            // OK
t("default 'N'");          // FAIL Expected "on", [ \t\n\r], [+\-], or [0-9] but "'" found.
t("default null");         // FAIL Expected "on", [ \t\n\r], [+\-], or [0-9] but "n" found.
t("default sysdate");      // FAIL Expected "on", [ \t\n\r], [+\-], or [0-9] but "s" found.
t("default sys_guid()");   // FAIL Expected "on", [ \t\n\r], [+\-], or [0-9] but "s" found.
t("default 0.5");          // FAIL Expected ")", ... or [0-9] but "." found.

Note that default 0.5 fails too:
integer matches the 0 and the . is then unexpected,
even though the grammar already has a number rule that handles it.

Most of the pieces are already there. literal (L2652) covers strings, numbers,
national character literals, q'[..]' quoting and datetime literals, it just is
not reachable from expr. Missing entirely are function calls, the datetime
keywords (sysdate, systimestamp, current_date, ...) and sequence
pseudocolumns (some_seq.nextval).

Where I ran into it: drawdb's "Import from SQL" with the Oracle dialect fails on
any table whose DDL carries a string default, which for a real schema is most of
them. drawdb also has a matching // TODO: reconstruct default when implemented in parser in its Oracle importer, so I assume this is known.

One thing that would help a consumer: literal normalises what it returns, so
the original spelling of a default is lost. Reporting the source text of the
default expression alongside it would let a consumer reproduce it verbatim.

Environment: oracle-sql-parser 0.1.0, Node v24.18.0.

Happy to open a PR if you would like — I have a branch that points expr at
literal and adds rules for the function/keyword/pseudocolumn forms, with tests.