SQL - Questions

Answer the following questions using the mobile phone company database. Submit only the SQL statements, NOT the query result!!

customer	calls	mobile	staff	tower	connection
customerID	callID	mobileID	staffID	towerID	connectID
surname	mobileID	phoneNumber	surname	location	towerID
givenName	phoneNumber	brandName	givenName	bandwidth	callID
dob	callDate	joinDate	sex	maxConn
sex	callDuration	cancelDate	joinDate
phoneHome		planName	resignDate
phoneWork		phoneColour	address		plan
phoneFax		customerID	suburb		planName
address		staffID	postcode		connectFee
suburb			phone		peakFee
state			supervisorID		offPeakFee
postcode			commission		weekendFee
			ratePerHour

i) What is the average age of all customers?

j) What is the total annual salary being paid out to current active staff? (Round the result to 2 decimal places.) (Assume 40 hours in a week and 52 weeks in a year.)

k) Show a list of brand names and a count of the unique customers for each brand.

l) For calls made in 1999, display how many calls were made on each day of the week.