Extensions
Partial Reading
For CSV files, files will be downloaded entirely in most cases, due to the row-based nature of the format.
For Parquet files, DuckDB supports [partial reading](#docs:data:parquet:overview::partial-reading), i.e., it can use a combination of the Parquet metadata and [HTTP range requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests) to only download the parts of the file that are actually required by the query. For example, the following query will only read the Parquet metadata and the data for the `column_a` column:  
```sql
SELECT column_a
FROM 'https://domain.tld/file.parquet';
```  
In some cases, no actual data needs to be read at all as they only require reading the metadata:  
```sql
SELECT count(*)
FROM 'https://domain.tld/file.parquet';
```