sql meta information generates wrong column info in some cases
```

In [6]: sq.sql_meta()
Out[6]: 
('SELECT t2."feature", SUM(t1."count") AS count FROM "featurecount" AS t1 INNER JOIN "feature" AS t2 ON t1."feature_id" = t2."id" GROUP BY t2."feature"',
 [],
 {'columns': [(models.FeatureCount, ('SUM', 'count', 'count')),
   (models.Feature, 'feature')],
  'graph': {models.FeatureCount: [(models.Feature, None, None)]}})
```

Should be:

```
'columns': [(models.Feature, 'feature'), (models.FeatureCount, ('SUM', 'count', 'count'))]
```

```
```
