Answer 1

I am not sure, but I think you have to select the book1.bno column too to make it work.

Answer 2

Do you really have two tables called book and book1? Sound strange.
If you are trying this in sololearn playground then it will surely not work as there is no SQL support here.

Answer 3

The best query is to use Join
for exemple
select t1.* , t2.* FROM table1 as t1 LEFT JOIN table2 AS t2 ON t1.id = t2.id WHERE t2.id IS NOT NULL