#39 union and bracket cause error

[johnzeng]

If post this SQL to TgaAdvancedSQLParser and parse it
will cause error.
cause error SQL:
(select aTable_GUID as GUID from bTable right outer join
aTable on bTable_ZBGUID=aTable_GUID)
union all
(select cTable_GUID as GUID from dTable right outer join
cTable on dTable_ZBGUID=cTable_GUID)

but if omit the bracket ,that all work well.