Can a composite index be considered ordered by the sequence of its elements?

A composite index in databases is an index created on multiple columns of a table.

It is structured in the order of the elements, meaning the order of columns in the index matters. The index is first sorted by the first column, then within the same values of the first — by the second, and so on.

This means that a composite index is effectively used for queries that filter or sort data based on the leading columns of the index in the same order.

For example, if there is an index on (A, B, C), it is well-suited for queries with conditions on A, on A and B, or on A, B, and C, but not efficient for queries only on B or C.

Thus, a composite index can be considered structured in the order of its elements, and this order is critical for its usage.