can we create number of fields at a time with same data type in mysql? alter table students 
 add s1,s2,s3,s4,s5,s6,s7 int;

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 's2,s3,s4,s5,s6,s7 int' at line 2
You can add several columns at once but you need to declare the types per column:

alter table t add column (s5 int, s6 int);


You can also use:

alter table t add (s5 int, s6 int);


but I prefer the first one. Note that the parentheses are mandantory.

You don't mention your version, but the syntax have been valid since at least 5.1:

http://dev.mysql.com/doc/refman/5.1/en/alter-table.html