Is it possible to explicitly specify the use of an index in the WHERE clause to speed up the search?

There is no universal syntax in SQL standard for explicitly specifying the use of a particular index in the WHERE clause. However, some DBMSs have special constructs or hints that allow directing the query optimizer to use a specific index.

For example, in MySQL, you can use the USE INDEX construct in the FROM clause:

SELECT * FROM table_name USE INDEX (index_name) WHERE condition;

In Oracle and other DBMSs, special comments with hints are used, for example:

SELECT /*+ INDEX(table_name index_name) */ * FROM table_name WHERE condition;

Thus, to explicitly specify index usage, you need to use syntax specific to the particular DBMS, rather than in the WHERE condition itself.