1) Delete vs Truncate vs Drop Delete deletes all/ a few the records of the table. Truncate deletes all the records of the table, where as drop deletes the table and any indexes,privileges associated with the table. Delete is a DML operation, takes more time as it can be rolled back so will store the data in the undo space where as Truncate and Drop are DDL statements and can not be rolled back, so they are faster. From Oracle 10 the database tables can be undroppped. FLASHBACK TABLE TABLE_NAME TO BEFORE DROP; 2) SQL Joins can be classified into Equi join and Non Equi join. 1) SQL Equi joins It is a simple sql join condition which uses the equal sign as the comparison operator. Two types of equi joins are SQL Outer join and SQL Inner join. For example: You can get the information about a customer who purchased a product and the quantity of product. 2) SQL Non equi joins It is a sql join condition which makes use of some comparison operator other than the equal sign like >,