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 Services table, find corresponding rows in Ref_Service_Types table and in Drama_Workshop_Groups table.
Step 2: find the number of different Currency_Code in the results of step 1 whose Service_Type_Description equals provide photo service

SOLUTION: SELECT Count ( DISTINCT T2.Currency_Code ) FROM Ref_Service_Types AS T1 JOIN Drama_Workshop_Groups AS T2 JOIN Services AS T3 ON T1.Service_Type_Code = T3.Service_Type_Code AND T3.Workshop_Group_ID = T2.Workshop_Group_ID WHERE T1.Service_Type_Description = "provide photo service"

PROBLEM: Step 1: For each row in Campuses table, find corresponding rows in csu_fees table and in faculty table.
Step 2: find the average CampusFee in the results of step 1 whose csu_fees's Year equals 2005 and Faculty equals 357.1

SOLUTION: SELECT Avg ( T2.CampusFee ) FROM Campuses AS T1 JOIN csu_fees AS T2 ON T2.Campus = T1.Id JOIN faculty AS T3 ON T1.Id = T3.Campus WHERE T2.Year = 2005 AND T3.Faculty = 357.1

PROBLEM: Step 1: find the DName of Department table.
Step 2: find the DName of Department table.
Step 3: show the rows that are in the results of step 1 but not in the results of step 2

SOLUTION:
SELECT DName FROM Department EXCEPT SELECT DName FROM Department