How to implement a combined index in a database to speed up searches?

A composite index is created in a database to speed up searches across multiple columns simultaneously. It is useful when queries filter or sort data based on several fields.

In SQL, it is created as follows:

CREATE INDEX idx_name ON table_name (column1, column2);

An example in Java using JDBC:

String sql = "CREATE INDEX idx_user_name ON users (last_name, first_name)";
try (Statement stmt = connection.createStatement()) {
    stmt.execute(sql);
}

It is important to remember that the order of columns in the index affects its efficiency: the index is most effective if queries filter first by the first column, then by the second, and so on.