partitioning could be seen as kind of index - it helps you to directly query the folder in partition which has relevant data leaving all other partition folder untouched.
there is another feature in data bricks Delta - Data Skipping. When writing data to Delta, the writer is collecting statistics (for example, min & max values) for first N columns (32 by default) and write that statistics into Delta log, so when we filter data by indexed column, we know if given file may contain given data or not. Another indexing technique for databricks delta is bloom filtering that is shows if the specific value is definitely not in the file, or could be in the file.
