http://ja.wikipedia.org/wiki/UPDATE_(SQL)#.E7.B5.90.E5.90.88
UPDATE t1 SET a1 = 2 FROM t2 WHERE t1.a2 = t2.b2 AND t2.b1 = 0;
http://ja.wikipedia.org/wiki/UPDATE_(SQL)#.E7.B5.90.E5.90.88
UPDATE t1 SET a1 = 2 FROM t2 WHERE t1.a2 = t2.b2 AND t2.b1 = 0;