Will using an indexed column speed up GROUP BY and ORDER BY operations?

Yes, an indexed column can speed up GROUP BY and ORDER BY operations, but with some caveats:

• For ORDER BY, an index is especially effective if the sorting is done on the indexed column in the same order as the index. Then the DBMS can use the index for quick sorting without an additional sorting step.

• For GROUP BY, an index can help if the grouping is done on indexed columns, as the data is already partially sorted and the DBMS can aggregate data faster.

However, the effectiveness depends on:

• The type of index (B-tree, Bitmap, etc.)
• The number of unique values in the column
• The volume of data and statistics

Example: if you have an index on the category column, the query

SELECT category, COUNT(*) FROM products GROUP BY category ORDER BY category;

can execute faster thanks to the index.