Tootfinder

Note:
SELECT *
FROM t1 INNER JOIN t2
ON concat(t1.a,t1.b,t1.c) =
concat(t2.a,t2.b,t2.c)
is much faster than
FROM t1 INNER JOIN t2
ON t1.a = t2.a AND t1.b = t2.b AND t3.a = t3.b
The ad hoc calculated key creates a hash join reducing the complexity to O(n)