Two single-column indexes vs one two-column index in MySQL?

Solution 1:

If you have two single column indexes, only one of them will be used in your example.

If you have an index with two columns, the query might be faster (you should measure). A two column index can also be used as a single column index, but only for the column listed first.

Sometimes it can be useful to have an index on (A,B) and another index on (B). This makes queries using either or both of the columns fast, but of course uses also more disk space.

When choosing the indexes, you also need to consider the effect on inserting, deleting and updating. More indexes = slower updates.

Solution 2:

A covering index like:

ALTER TABLE your_table ADD INDEX (giver_id, recipient_id);

...would mean that the index could be used if a query referred to giver_id, or a combination of giver_id and recipient_id. Mind that index criteria is leftmost based - a query referring to only recipient_id would not be able to use the covering index in the statement I provided.

Please note that some older MySQL versions can only use one index per SELECT so a covering index would be the best means of optimizing your queries.