#46 Bad SQL generation for UNIONs

[Aurélien Bénel]

The following query doesn't work with the DbModel:
SELECT ?attribute ?value WHERE {
{
<http://acme.com/foo#bar>
?attribute
?node
.
?node
<http://acme.com/bar#toMember>
?value .
} UNION {
<http://acme.com/foo#bar>
?attribute
?value .
}
}

It generates the following fatal error :
Uncaught exception 'Exception' with message 'ADOdb error: Unknown column 't0.predicate' in 'field list'

I looked at the generated SQL and there is definitely a problem:
SELECT
t0.predicate as "t0.value_v_attribute",
t1.object as "t1.value_v_value",
t1.object_is as "t1.is_v_value",
t1.l_language as "t1.lang_v_value",
t1.l_datatype as "t1.type_v_value"
...
FROM statements as t0 LEFT JOIN statements as t1
...
UNION
...
SELECT
t0.predicate as "t0.value_v_attribute",
t1.object as "t1.value_v_value",
t1.object_is as "t1.is_v_value",
t1.l_language as "t1.lang_v_value",
t1.l_datatype as "t1.type_v_value"
...
FROM statements as t1
...

The columns definitions should be different from one SELECT to the others.