Question 39: Which of the alternatives below actually work?

 
Imagine you have to create a running number for a query result and select only the line 1, 2 and 18.
You choose user variables as a means to do that.
 
(Find all correct answers)
 

a) set @a=0;
      select *
      from (select (@a:=@a+1) as ln,table_name
              from information_schema.tables
              where table_schema='mysql' order by table_name) v1
      where ln in (1,2,18);
 
b) set @a=0;
    select (@a:=@a+1) as ln,table_name
      from information_schema.tables
      where table_schema='mysql' and @a in (1,2,18)
      order by table_name;
 
c) set @a=0;
    select @a as ln,table_name
      from information_schema.tables
      where table_schema='mysql' having (@a:=@a+1) in (1,2,18)
      order by table_name; 

 
[ User Variables (5%) - User Variable Properties ]