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.

Step 1: find the department_name of Departments table.
Step 2: find the staff_id of Staff_Department_Assignments table whose date_assigned_to less than the results of step 1
SELECT T1.staff_id FROM Staff_Department_Assignments AS T1 WHERE T1.date_assigned_to < ( SELECT T2.department_name FROM Departments AS T2 )

Step 1: For each row in files table, find the corresponding rows in song table.
Step 2: find the average duration in the results of step 1 whose resolution less than 800
SELECT Avg ( T1.duration ) FROM files AS T1 JOIN song AS T2 ON T1.f_id = T2.f_id WHERE T2.resolution < 800

Step 1: find the number of rows of each value of first_name in employees table.
Step 2: find first_name, last_name of employees table with largest value in the results of step 1

SELECT first_name , last_name FROM employees GROUP BY first_name ORDER BY Count ( * ) Desc LIMIT 1