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Data Normalization Mult joins to one table

Good morning Experts.

I was looking at a simple'ish database today and came across a problem with trying to join one table to another multiple times. For this example, I was thinking of a Stat's program for a football team.

Table 1 is a "roster"
Roster_ID
Roster_number
roster_name

(this can be more complicated, but gives you an idea)

Table two would contain the "Plays" that the teams ran, lets say I want to list that one of the players passed the ball to another
Plays:
Play_ID
play_Down
play_PassBy (FK connected to roster table)
play_catchBy(FK Connected to roster table)
play_runby (FK Conneted to roster table)

I would not be able to join each of the passby/catchby/runby back to the same roster table, can I?

Some plays will have values in the catchby and runby, so most joins will either show one value or another - how would you write a query to get around this?

Thank you - I hope my example gives you the details you need to figure out what I'm talking about! :)

BigSchmuh

Your Stat query can be like the below SQL:

SELECT r.Roster_number, r.roster_name, Sum(CASE WHEN r.Roster_ID = p.play_PassBy THEN 1 ELSE 0 END) NbPass , Sum(CASE WHEN r.Roster_ID = p.play_catchBy THEN 1 ELSE 0 END) NbCatch, Sum(CASE WHEN r.Roster_ID = p.play_runby THEN 1 ELSE 0 END) NbRun
FROM Plays p INNER JOIN Roster r ON r.Roster_ID in (p.play_PassBy, p.play_catchBy, p.play_runby)
GROUP BY r.Roster_number, r.roster_name

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ste5an

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Hamed Nasr

Think of it as:
3 views from roaster table.
roaster_PassBy
roaster_catchBy
roaster_runby

Join the views to the Plays table relating the respective fields.

The same effect can be achieved using aliasses to the table. (From table alias)

hej613

ASKER

Obviously I need to go to Join school again - I'm not 100% sure on why these work... on #1 there is a case statement, and I'm not sure what the point is of returning 1/0....

number 2 I only see it "FROM" being one table, and then the second table named on the join...

ste5an

It's quite simple: Although each join specification joins only two tables, a FROM clause can contain multiple join specifications. This allows many tables to be joined for a single query. Or in your case to use the same table to join multiple times to retrieve different data.

BigSchmuh

#1: Summing 1 and 0 allows you to account each Roster for his Pass/Catch/Run

Sean Stuber

can you give some sample data and expected output?

the above examples show how various joins "could" be done, but we're all just guessing as to what kind of results you're looking for.

hej613

ASKER

Absolutely - Here is a quick example I threw together: (Thanks all for the different examples!)

CREATE TABLE STATS.ROSTER
(
  R_ID        NUMBER                            NOT NULL,
  R_NUM       NUMBER,
  R_NAME      VARCHAR2(50 BYTE),
  R_POSITION  VARCHAR2(20 BYTE)
)


CREATE TABLE STATS.OFF_PLAY
(
  P_ID            NUMBER                        NOT NULL,
  P_GAME          NUMBER,
  P_DOWN          VARCHAR2(15 BYTE)             NOT NULL,
  P_TYPE          VARCHAR2(5 BYTE),
  P_LOCATION      VARCHAR2(15 BYTE),
  P_RUNBY         NUMBER,
  P_THROWBY       NUMBER,
  P_CATCHBY       NUMBER,
  P_YARDS         NUMBER,
  P_SCORETYPE     VARCHAR2(10 BYTE),
  P_POINTS        VARCHAR2(1 BYTE),
  P_FUMBLE        VARCHAR2(1 BYTE),
  P_INTERCEPTION  VARCHAR2(1 BYTE),
  P_COMPLETION    VARCHAR2(1 BYTE),
  P_INCOMPLETE    VARCHAR2(1 BYTE),
  P_BALLLOC       VARCHAR2(3 BYTE),
  P_BALLYRD       NUMBER
)

Example roster information:

r_id    r_num      r_name             r_position
1	4	Caleb N	
2	7	Mark R	
3	10	Dillon W	          QB
4	14	Kyle K          	RB SS
5	20	Dustin J	
6	21	Jordan Sellers	RB WR

insert into off_play
VALUES (4, 1, 1,'P','L_OT_L','',3,9,12,'NA','','','','','','OWN','34';);
insert into off_play
VALUES (3, 1, 2,'P','L_OT_L','',5,6,12,'NA','','','','','','OWN','34';);

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hej613

ASKER

If you notice on this example - on p_id#4 there is a value for catchby and throwby (both linking over to the roster table) in my experimentation I would get a value in one of these, but not the other.

Sean Stuber

>>> in my experimentation I would get a value in one of these, but not the other.

is that desired? or not?

given the data above, what do you "want" returned?

hej613

ASKER

I would want to see both names, I would want to know player in rosters r_id #3 (r_num 10, dillian w) threw to #9 and show details of both names in the query....

SOLUTION

Sean Stuber

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