Table: eccc_1999
Columns: team
tries_for
tries_against
try_diff
points_for
points_against
points_diff

Question: Which Tries against has Points against larger than 156, and Points for of 127, and Tries for larger than 17?
SQL: SELECT AVG("tries_against") FROM eccc_1999 WHERE "points_against" > 156 AND "points_for" = 127 AND "tries_for" > 17

Question: Which Try diff has Tries for of 12?
SQL: SELECT "try_diff" FROM eccc_1999 WHERE "tries_for" = 12