Question: WHAT IS THE SOURCE WITH A TYPE OF Transfer AND MEX?
SQL: SELECT "Source" FROM "2-17686681-3" WHERE "Type" = 'Transfer' AND "Nat." = 'MEX';

Question: WHAT IS THE NAME WITH Bayer Leverkusen?
SQL: SELECT "Name" FROM "2-17686681-3" WHERE "Moving to" = 'Bayer Leverkusen';

Question: WHAT NAME HAS A Free TRANSFER Free AND Retired?
SQL: SELECT "Name" FROM "2-17686681-3" WHERE "Transfer fee" = 'Free' AND "Moving to" = 'Retired';

Question: WHAT Transfer FEE HAS A TYPE OF Transfer FOR Dos Santos?
SQL: SELECT "Transfer fee" FROM "2-17686681-3" WHERE "Type" = 'Transfer' AND "Name" = 'Dos Santos';