==== Tests of SQL - different ways to writing the same SPARQL query.

UniProt

explain 
  ex1a-alt.sql
Why does more joins work faster???

Why does adding an unused variable speed the query up?

Try:
1/ Just use   FROM T1, T2 ... WHERE ...
2/ Use (SELECT ...) for the constants
3/ Reorder

STRAIGHT_JOIN to avoid the optimizer.