No output at all still leaks everything, one yes/no question at a time, through boolean or timing oracles.

Blind SQL injection

No results, no errors: you still have a yes/no oracle.

• Boolean-blind. ' AND SUBSTRING((SELECT password FROM users LIMIT 1),1,1)='a changes the page when the guess is right. Binary-search each character.
• Time-blind. When even the page does not change, make the server wait: ' AND IF(SUBSTRING(...)='a', SLEEP(3), 0)-- . A slow response means yes.