Hi Peter,

it depends on the way you access your tables. For example a count operation is for me a reason to insert all indexes need to gain a fully optimizable query, unless there's some severe impact on other queries. On the other hand, if the main access key is something that is highly distributed, like a customer ID, or any other primary or foreign key, there's often not much need for additional indexes.

In your example, if I need all "D" reservations from last week, I'd probably only create an index on the date, but if I need all "D" reservation in the entire table, I'd add an index on the reservation type. If I have to count the number of different reservation types last week, I'd add an index on both fields.

Christof