Convert table of individual events-distances into a summary table of events - mysql

Question

Two weeks ago I started learning SQL and it has been going pretty good so far but I have run into a situation that I can't seem to resolve. After two days of searching the web and looking at books, I am no closer to solving this issue, so time to ask for some help. Part of my problem is that being so new to SQL I'm not exactly sure what to search for.
This is using mySQL and INNODB.
After some joins and other things I have the table below with athlete information giving the type of event in which the athlete participated and the distance of that event. The possible event/distance combinations are {A10,A15,B10,B15}.
Events Table
last_name first_name event distance
Munster Eddie A 10
Brady Marsha A 10
Clampet Jethro B 15
Grumby Jonas A 15
Brady Peter A 10
Brady Marsha A 10
Brady Marsha B 15
Grant Ginger B 15
Munster Eddie B 10
Brady Marsha A 10
What I am trying to do as the final step is to transform this table into a form that shows how many times each athlete participated in each event, like the following output:
last_name first_name A10 A15 B10 B15
Munster Eddie 1 0 1 0
Brady Marsha 3 0 0 1
Clampet Jethro 0 0 0 1
Grumby Jonas 0 1 0 0
Brady Peter 1 0 0 0
Grant Ginger 0 0 0 1
I think I want to use correlated subqueries, so I have tried a number variants of this following SQL query but it returns "Operand should contain 1 column(s)", which makes sense.
SELECT last_name, first_name,
count(if(event='A',1,0) AND if(distance=10,1,0)) AS A10
FROM sample s
WHERE (SELECT last_name, first_name, event, distance
FROM sample s1
WHERE s1.last_name = s.last_name
)
ORDER BY last_name, first_name;
The steps I see I need are:
1. create a set of each name in the table, which I can do, and then
2. iterate through each name, creating a new query selecting event/distance and then
3. summing that query on event/distance combination;
4. return the result back up to #1.
I see that procedures provide some looping capabilities, is that the way to do this? Is what I want to do possible in the SQL environment? My next step is to just dump the raw table to PHP and process it there.
Any thoughts and/or solutions are greatly appreciated.

Answer 1

Add GROUP BY:
SELECT last_name,
first_name,
count(if(event = 'A', 1, NULL)
AND if(distance = 10, 1, NULL)) AS A10,
count(if(event = 'A', 1, NULL)
AND if(distance = 15, 1, NULL)) AS A15,
count(if(event = 'B', 1, NULL)
AND if(distance = 10, 1, NULL)) AS B10,
count(if(event = 'B', 1, NULL)
AND if(distance = 15, 1, NULL)) AS B15
FROM sample s
GROUP BY last_name,
first_name
ORDER BY last_name,
first_name;

Answer 2

I would suggest using the SUM + CASE syntax.
Try something like this:
SELECT LAST_NAME,
FIRST_NAME,
SUM(CASE
WHEN EVENT = 'A'
AND DISTANCE = 10 THEN 1
ELSE 0
END) AS A10,
SUM(CASE
WHEN EVENT = 'A'
AND DISTANCE = 15 THEN 1
ELSE 0
END) AS A15,
SUM(CASE
WHEN EVENT = 'B'
AND DISTANCE = 10 THEN 1
ELSE 0
END) AS B10,
SUM(CASE
WHEN EVENT = 'B'
AND DISTANCE = 15 THEN 1
ELSE 0
END) AS B15
FROM SAMPLE
GROUP BY LAST_NAME,
FIRST_NAME
You can find a working example on SQL Fiddle.
Good Luck!