Consider a database consisting of the following tables (relations): SAILORS(sid, name, rating, age)

BOATS(bid, name, color)

RESERVED(sid, bid, day). Write SQL statement for each of the following queries.

(17) For each color, find the number of boats in the color.

(18) For each boat, find the bid and the average age of sailors who reserved it.

(19) Find the number of boats reserved by Smith.

(20) For each sailor, find the sid and the number of boats reserved by the sailor.