Fix!: traverse union scopes iteratively

[georgesittas]

No description provided.

[tobymao]

does this work now? should we add a test like

from sqlglot import parse_one
from sqlglot.optimizer.scope import build_scope

sql = "SELECT 1 UNION ALL " * 10000
sql += "SELECT 1"

q = parse_one(sql)

build_scope(q)

[georgesittas]

yep it works

[georgesittas]

Hmm, the traversal though is still problematic...

>>> from sqlglot import exp, parse_one
>>> from sqlglot.optimizer.scope import build_scope
>>>
>>> large_union = parse_one(" UNION ALL ".join(["SELECT x FROM t"] * 1000))
>>> len(list(large_union.find_all(exp.Select)))
1000
>>>
>>> scope = build_scope(large_union) # ok
>>> for s in scope.traverse():
...     print(s)
...
    for child_scope in itertools.chain(
RecursionError: maximum recursion depth exceeded while calling a Python object