Re^4: Avoiding SQL double jeopardy

[GrandFather]

The big picture is we have a weekly "experience exchange" in our development team. Each week we offer a topic we are prepared to teach for 3/4 of an hour. Then at the appointed time we pair up as teacher/learner for our weekly session. Over time it is expected that we spend about as many sessions teaching as learning.

At present the process is mediated by post it notes stuck to a wall. The script is intended to replace the post it note scrum and help ensure everyone gets a more or less equal opportunity to teach and learn.

So, a person can only be in each session once. For any session a person may be a teacher or a learner. There will only ever be teacher and learner roles. Each session includes everyone who is available.

The query at the heart of the issue is to find all pending session pairings an individual or group of individuals are involved in.

[Pope-O-Matik]

Thank you, i think i got it now. :) Two more clarifications, though: Can there be more than one teacher per session? Can there be more than one student per session? That is, "by definition" as opposed to how it just happens to work out.

[GrandFather]

Hmmm there is a little confusion of nomenclature (my fault). Properly speaking we have one XR (eXperience Replication) session a week. People pair up as a teacher and learner. If there is an odd number of people one "pair" will have one teacher and two learners.

The current Sessions table identifies sessions by DrawDate and contains a "SessionId" which I should rename to PairId. There will be multiple pairs per weekly session.

PairId is unique in the Sessions table but there will be multiple entries (generally two) in the SessPeople table (which I should rename to the Pairs table) for each PairId.

[Pope-O-Matik]

Okay, so always on teacher, 1 or more Learners.

Are subjects a set thing? That is, only a limited amount of subjects (expanded at will), or can it be anything, that is, just a quick note.

I don't believe you need a session id. As one person can only teach one session at a time, the natural key is Teacher/Time. And for Person, shouldn't it be employee? And, do Employees already have unique id, such as their company email address?

[Pope-O-Matik]

Here's an attempt at it:

CREATE TABLE Employee
(
 Id        NUMBER        PRIMARY KEY AUTOINCREMENT,
 First_Name    TEXT,
 Last_Name    TEXT
);

CREATE TABLE Topic
(
 Name        TEXT CHECK(Name = LOWER(Name)) PRIMARY KEY,
 Description    TEXT
);

CREATE TABLE Session
(
 Teacher    INTEGER                REFERENCES Employee,
 Start        DATETIME,
 Finish        DATETIME,
 Topic        TEXT        NOT NULL    REFERENCES Topic,
 PRIMARY KEY(Teacher, Start)
);

CREATE TABLE Session_Learner
(
 Teacher    NUMBER,
 Start        DATETIME,
 Learner    NUMBER        NOT NULL    REFERENCES Employee,
 --
 FOREIGN KEY(Teacher, Start) REFERENCES Session,
 PRIMARY KEY(Teacher, Start, Learner)
);

CREATE VIEW
    Session_Employee
AS
    WITH
        Session_Teacher_Learner
    AS
        (
         SELECT
             Session.Teacher,
             Session.Start,
             Session.Topic,
             Session_Learner.Learner
         FROM
             Session,
             Session_Learner
         WHERE
             Session_Learner.Teacher    = Session.Teacher
           AND    Session_Learner.Start    = Session.Start
        )
    SELECT
        Teacher,
        Start,
        Topic,
        Teacher Employee
    FROM
        Session_Teacher_Learner
    UNION ALL
    SELECT
        Teacher,
        Start,
        Topic,
        Learner
    FROM
        Session_Teacher_Learner;