How to comment on SQL queries?

Which statement is used to access an existing Database? 

To create a database only if it doesn’t already exist, which clause is used? 

The facility that allows nesting one select statement into another is called __________ 

The number of rows in the table is 100. Suppose all rows are deleted. The new row starts with sequence number _____________ 

Which mode tells the server to recognize double quote as an identifier quoting character? 

Which SQL command is used to retrieve all records from a table?

 Which clause in the SQL standard controls how NULL values in a composite foreign key are handled when comparing to a primary key.
 

 Which mode is used to turn off the special meaning of backslash and treat it as an ordinary character? 

 What will happen if the data being loaded into a text column exceeds the maximum size of that type?