SQL statement of Delete and Drop Help?

1. How do we select all records from the table using SQL statements? Write the syntax. 
2. In which situation do we prefer DELETE command to delete a table instead of using DROP command?
3. Explain the four advantages and disadvantages of the De-normalization.

1. Select * from table_name;
2. DELETE command is used to delete some record from a table, and DROP table is used to delete whole table from the database.
3. Denormalization has these disadvantages: 

• Denormalization usually speeds retrieval but can slow updates. This is not a real concern in a DSS environment.
• Denormalization is always application-specific and needs to be re-evaluated if the application changes. 
• Denormalization can increase the size of tables. 
• In some instances, denormalization simplifies coding; in others, it makes it more complex.