The database is a collection of data and this data is stored in form of tables at logical level, and in the data files at the physical level. There are some other files as well like Redo log files, Control files, Initialization files which stores important information about the database.
No, you can't drop all the columns of a table. one data column must be available in the table. To drop all the columns you have to drop the entire table. To Drop columns one at a time, you can use the below syntax. ALTER TABLE table_name DROP COLUMN column_name
Query:- SELECT Emp_Name,Emp_Salary FROM Employee e1 WHERE 2 = (SELECT COUNT(DISTINCT (e2.Emp_Salary))FROM Employee e2 WHERE e2.Emp_Salary >= e1.Emp_Salary) The above employee table contains two same records as second highest salary so the result set will look like below output table. Output:- Emp_Name Emp_Salary Sham 15000