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Can I get this all in one query?

From: "Richard Rowell" <the_pitman(at)hotmail(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: Can I get this all in one query?
Date: 2000-08-28 07:56:05
Message-ID: 39aa0b25_2@news.shreve.net (view raw or flat)
Thread:
Lists: pgsql-sql
I'm designing a database/website that will allow students to "grade" the professors/classes the students attend.
There are eight different "factors" that the students assign grades on.  Until tonight I had one table that kept the
scores assigned by students.  This table name REVIEW had a field named for each factor.  IE:

CREATE TABLE review(
class_uid         INTEGER                       REFERENCES class,
student           VARCHAR(20)                   REFERENCES student,
snooze           INTEGER, 
professional     INTEGER,
personality       INTEGER,
grading            INTEGER,
effectiveness    INTEGER,
knowledge       INTEGER,
accent            INTEGER,
enthusiasism    INTEGER,

uid                 SERIAL                  PRIMARY KEY,
UNIQUE(class_uid,student)
)

THis allowed me to write simple queries that would pull averages for a college,department, a course, a professor,
etc.  Example query:

//Returns averages in all 8 factors of every department
SELECT crs.dept AS department,
       ROUND(AVG(CAST(rvw.snooze        AS FLOAT)) ,2) AS snooze,
       ROUND(AVG(CAST(rvw.professional  AS FLOAT)) ,2) AS professional,
       ROUND(AVG(CAST(rvw.personality   AS FLOAT)) ,2) AS personality,
       ROUND(AVG(CAST(rvw.grading       AS FLOAT)) ,2) AS grading,
       ROUND(AVG(CAST(rvw.effectiveness AS FLOAT)) ,2) AS effectiveness,
       ROUND(AVG(CAST(rvw.knowledge     AS FLOAT)) ,2) AS knowledge,
       ROUND(AVG(CAST(rvw.accent        AS FLOAT)) ,2) AS accent,
       ROUND(AVG(CAST(rvw.enthusiasism  AS FLOAT)) ,2) AS enthusiasism
  FROM review rvw, class cls, course crs
  WHERE rvw.class_uid=cls.uid AND cls.course_uid=crs.uid
  GROUP BY crs.dept;

However, in a developer meating tonight it was decided that the factors (which are in another table in the database)
should not be "hard coded" into the review table, but rather a new table should be created implementin the many to
many relationship.  The revised review table(s) looks like so:

CREATE TABLE review
(
  class_uid         INTEGER                       REFERENCES class,
  student           VARCHAR(30)                   REFERENCES student,
  comments          TEXT,

  uid               SERIAL                        PRIMARY KEY,
  UNIQUE(class_uid,student)
);

CREATE TABLE review_scores
(
  review_uid        INTEGER                       REFERENCES review,
  factor            VARCHAR(30)                   REFERENCES factor,
  score             INTEGER,

  uid               SERIAL                        PRIMARY KEY,
  UNIQUE(review_uid,factor)
);

My problem is now I do not know how to write a single query that can pull the average of all 8 factors at once,
grouped my department as above.  If it is a specific department it is trivial, but for all departments at once I would
need to use two group by statements in the same SQL query.

I'm sure there is a simple solution, possibly using sub-queries which I'm not very farmiliar with.  I am attaching the
database schema below in case it would make things clearer.

TIA!

CREATE TABLE term
(
  name              VARCHAR(30)                   PRIMARY KEY
);

CREATE TABLE semester
(
  term              VARCHAR(30)                   REFERENCES term         ON UPDATE CASCADE,
  year              INTEGER,
  locked	    BOOLEAN	  DEFAULT TRUE,

  uid               SERIAL                        PRIMARY KEY,
  UNIQUE(term,year)
);

CREATE TABLE college
(
  name              VARCHAR(30)                   PRIMARY KEY
);

CREATE TABLE department
(
  department_id     VARCHAR(4)                    PRIMARY KEY,
  name              VARCHAR(30)   NOT NULL,
  college           VARCHAR(30)                   REFERENCES college       ON UPDATE CASCADE
);

CREATE TABLE degree
(
  name              VARCHAR(30)                   PRIMARY KEY
);

CREATE TABLE professor
(
  first_name        VARCHAR(30)   NOT NULL,
  last_name         VARCHAR(30)   NOT NULL,
  email_address     VARCHAR(30),
  degree_type       VARCHAR(30)                   REFERENCES degree,
  undergrad_univ    VARCHAR(50),
  grad_univ         VARCHAR(50),
  major             VARCHAR(20),
  comment	    TEXT,

  uid               SERIAL                        PRIMARY KEY
);

CREATE TABLE professor_department_link
(
  prof_uid	    INTEGER			  REFERENCES professor,
  dept		    VARCHAR(4)			  REFERENCES department,
  UNIQUE(prof_uid,dept)
);

CREATE TABLE email_domain
(
  domain            VARCHAR(20)                   PRIMARY KEY
);

CREATE TABLE student
(
  passwd            VARCHAR(30)   NOT NULL,
  email_prefix      VARCHAR(30)   NOT NULL,
  email_domain      VARCHAR(20)                   REFERENCES email_domain ON UPDATE CASCADE,
  authenticated     BOOLEAN       DEFAULT FALSE,

  screen_name       VARCHAR(20)                   PRIMARY KEY,
  UNIQUE(email_prefix,email_domain)
);

CREATE TABLE course
(
  dept        VARCHAR(4)                    REFERENCES department    ON UPDATE CASCADE,
  course_number     VARCHAR(8),
  description	    VARCHAR(100),

  uid               SERIAL                        PRIMARY KEY,
  UNIQUE(dept,course_number,description)
);

CREATE TABLE class
(
  course_uid        INTEGER                       REFERENCES course,
  prof_uid     INTEGER                       REFERENCES professor,
  semester_uid	    INTEGER			  REFERENCES semester,

  uid               SERIAL                        PRIMARY KEY,
  UNIQUE (course_uid, prof_uid, semester_uid)
);

CREATE TABLE review
(
  class_uid         INTEGER                       REFERENCES class,
  student           VARCHAR(30)                   REFERENCES student,
  comments          TEXT,

  uid		    SERIAL			  PRIMARY KEY,    
  UNIQUE(class_uid,student)
);

CREATE TABLE review_scores
(
  review_uid        INTEGER                       REFERENCES review,
  factor            VARCHAR(30)                   REFERENCES factor,
  score             INTEGER,

  uid               SERIAL                        PRIMARY KEY,
  UNIQUE(review_uid,factor)
);

CREATE TABLE factor
(
  name              VARCHAR(30)                   PRIMARY KEY,
  description       TEXT,
  a_description     TEXT,
  b_description     TEXT,
  c_description     TEXT,
  d_description     TEXT,
  f_description     TEXT,
);



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Subject: Argument variables for select
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