sql commands.txt

http://sqlfiddle.com/#!5/2a3e4/8

** SCHEMA **

CREATE TABLE requests
(
  script_id int,
  time_stamp timestamp,
  requests int
);

CREATE TABLE scripts
(
  customer_id int,
  script_id int,
  version varchar (255),
  event varchar (255)
);

INSERT INTO requests 
(script_id,time_stamp,requests)
VALUES 
(32,"2015-05-01 10:00:00",154),
(33,"2015-05-01 10:00:00",432),
(32,"2015-05-01 10:00:05",243);

INSERT INTO scripts
(customer_id,script_id,version,event)
VALUES 
(104,32,1.7,"load"),
(159,33,1.7,"unload"),
(177,34,2.0,"unload"),
(104,35,2.0,"unload"),
(159,36,2.0,"load");
****

** TASKS **
1. SELECT * FROM script WHERE event = "load";

2. SELECT script.version, script.event, SUM(request.requests) FROM request, script 
WHERE script.script_id = request.script_id AND DATE(request.time_stamp) = "2015-05-01"
GROUP BY 1, 2;

3. SELECT script.version, script.event, SUM(request.requests) FROM request, script 
WHERE script.script_id = request.script_id AND script.customer_id = 104
GROUP BY 1, 2;

Question 1:
Some scripts are missing because the query will return only scripts that appear in the table requests. Meaning that it will return only script ids that generated requests.

Question 2:
SELECT COUNT(a.script_id), event
FROM scripts AS a 
LEFT JOIN requests AS b ON a.script_id = b.script_id
WHERE b.script_id IS NULL
GROUP BY event;