CTEs not completely extracted from successive UNION expressions

[Tiepies]

When creating a query that contains more than one UNION expression, CTEs do not get fully extracted to the start of the generated SQL query, resulting in a syntax error:

t = con.table('functional_alltypes')
expr1 = (t.group_by(['tinyint_col', 'string_col']).aggregate(t.double_col.sum().name('metric')))
expr2 = expr1.view()
join1 = (expr1.join(expr2, expr1.string_col == expr2.string_col)[[expr1]])
join2 = join1.view()
join3 = join1.view()
expr = join1.union(join2).union(join3)

impala.error.HiveServer2Error: AnalysisException: Syntax error in line 12:
WITH t0 AS (
^
Encountered: WITH
Expected: INSERT, SELECT, UPSERT, VALUES, COMMA

CAUSED BY: Exception: Syntax error

[cpcloud]

Thanks for the report. Marked as a bug for 0.14.0.