TASK DEFINITION: In this task you are expected to fix an SQL query based on feedback. You will be given an SQL statement and an English description with what is wrong about that SQL statement. You must correct the SQL statement based off of the feedback. 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: SQL: SELECT T2.LastName FROM Customer AS T1 JOIN Employee AS T2 ON T1.SupportRepId = T2.EmployeeId GROUP BY T1.SupportRepId HAVING Count ( * ) < = 20
Feedback: should find CUSTOMER's last name

SOLUTION: SELECT T1.LastName FROM CUSTOMER AS T1 JOIN EMPLOYEE AS T2 ON T1.SupportRepId  =  T2.EmployeeId GROUP BY T1.SupportRepId HAVING COUNT(*)  <=  20

PROBLEM: SQL: SELECT T1.characteristic_name FROM Characteristics AS T1 JOIN Products AS T2 JOIN Product_Characteristics AS T3 ON T1.characteristic_id = T3.characteristic_id AND T3.product_id = T2.product_id WHERE T2.product_name = "Herbs"
Feedback: Replace product characteristics , characteristic name and product name with reference product categories , unit of measure and product category code . Remove "in characteristics table and".

SOLUTION: SELECT unit_of_measure FROM ref_product_categories WHERE product_category_code  =  "Herbs"

PROBLEM: SQL: SELECT Count ( * ) FROM Student WHERE Fname = "Bootup Baltimore" AND Age > 18
Feedback: Replace first name with club name .

SOLUTION:
SELECT count(*) FROM club AS t1 JOIN member_of_club AS t2 ON t1.clubid  =  t2.clubid JOIN student AS t3 ON t2.stuid  =  t3.stuid WHERE t1.clubname  =  "Bootup Baltimore" AND t3.age  >  18