TASK DEFINITION: In this task you are expected to provide an SQL statement from an english description of what that SQL statement does. The description may include multiple steps but you should only ouput one SQL statement that accomplishes every step. An SQL query works by selecting data from a table where certain conditions apply. A table contains columns where every row in that table must have a value for each column. Every table has a primary key that uniquely identifies each row, usually an id. To choose which columns are returned you specify that after the "SELECT" statement. Next, you use a "FROM" statement to specify what tables you want to select the data from. When you specify a table you can rename it with the "AS" statement. You can reference that table by whatever name follows the "AS" statement. If you want to select data from multiple tables you need to use the "JOIN" statement. This will join the tables together by pairing a row in one table with every row in the other table (Cartesian Product). To limit the number of rows returned you should use the "ON" statement. This will only return rows where the condition specified after the statement is true, this is usually an equals operator with primary keys. You can also use the "WHERE" statement to specify that only rows with column values statisfying a certain condition, should be returned. The "GROUP BY" statement will group rows together that have equal column values for whatever columns follows the statement. The "HAVING" statement will return groups that statisfy whatever condition follows the statement. Any column(s) being returned from grouped rows must either be an aggregate function, (AVG, MAX, COUNT, SUM, ...) of a column, or the column(s) that the data was grouped by. To sort the returned data you can use the "ORDER BY" command which will order the data by whatever aggregate function or column follows the statement. The "DESC" statement will sort in descending order and the "ASC" statement will sort in ascending order. Finally, you can use the "LIMIT" statement to return a certain number of rows. When "*" is used in an SQL statement every column is returned. For example, SELECT * FROM table WHERE attribute = 1, will select every column from rows with the attribute column equal to 1.
PROBLEM: Step 1: For each row in Discount_Coupons table, find the corresponding rows in Customers table.
Step 2: find coupon_amount of the results of step 1 whose first_name equals good.
Step 3: find coupon_amount of the results of step 1 whose first_name equals bad.
Step 4: show the rows that are in both the results of step 2 and the results of step 3

SOLUTION: SELECT T1.coupon_amount FROM Discount_Coupons AS T1 JOIN Customers AS T2 ON T1.coupon_id = T2.coupon_id WHERE T2.first_name = "good" INTERSECT SELECT T1.coupon_amount FROM Discount_Coupons AS T1 JOIN Customers AS T2 ON T1.coupon_id = T2.coupon_id WHERE T2.first_name = "bad"

PROBLEM: Step 1: For each row in Product table, find the corresponding rows in Problems table.
Step 2: find rows in the results of step 1 whose problem_id greater than 1986-11-13.
Step 3: find each value of Product's product_id the results of step 1 along with the number of the corresponding rows to each value

SOLUTION: SELECT Count ( * ) , T1.product_id FROM Product AS T1 JOIN Problems AS T2 ON T1.product_id = T2.product_id WHERE T2.problem_id > "1986-11-13" GROUP BY T1.product_id

PROBLEM: find the number of rows in Reservations table whose LastName equals ROY

SOLUTION:
SELECT Count ( * ) FROM Reservations WHERE LastName = "ROY"