Does not find columns inside 'SUM-CASE-WHEN' pattern

Take this query:

`SELECT CAST(SUM(CASE WHEN segment = 'Premium' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) AS premiumpercentage FROM gasstations WHERE country = 'SVK'
`

The output is:

```
tables: ['gasstations']
columns: ['country']
```

Column 'segment' is missing.