存儲過程postgresql返回重複列

Question

我想做一個存儲過程來制定學生的日程安排，取決於他們正在採取什麼類（顯然）。不過，我相信這些連接會導致存儲過程返回兩倍的行數。

 

    CREATE OR REPLACE FUNCTION generateStudentSchedule(TEXT, REFCURSOR) RETURNS refcursor AS 
    $$ 
    DECLARE 
     tfname TEXT  := $1; 
     ref REFCURSOR := $2; 
    BEGIN 
     OPEN ref FOR 
     SELECT c.courseName, l.day, l.startTime, l.endTime 
     FROM ClassEvent l 
     JOIN Sections s ON l.courseID = s.courseID 
     JOIN Courses c ON l.courseID = c.courseID 
     JOIN Enrollment e ON e.courseID = l.courseID 
     WHERE (e.studentID IN (SELECT studentID 
        FROM Students 
        WHERE studentID IN (SELECT pid 
           FROM People 
           WHERE fname = tfname)) 
     AND l.sectionNumber = e.sectionNumber) 
     ORDER BY 
     CASE 
      WHEN l.day = 'Monday' THEN 1 
      WHEN l.day = 'Tuesday' THEN 2 
      WHEN l.day = 'Wednesday' THEN 3 
      WHEN l.day = 'Thursday' THEN 4 
      WHEN l.day = 'Friday' THEN 5 
     END ASC, l.starttime; 
     RETURN ref; 
    END 
    $$ 
    LANGUAGE plpgsql; 

這是輸出： output

關於如何解決此問題有什麼建議？

這裏是我的數據庫的表

 

    -- HOLDS A SPECIFIC COURSE WITHOUT THE INSTANCES OF THE CLASS -- 
    CREATE TABLE Courses (
     courseID  SERIAL  UNIQUE NOT NULL, 
     department TEXT    NOT NULL, 
     courseNumber VARCHAR(10)  NOT NULL, 
     courseName TEXT  UNIQUE NOT NULL, 
     credits  INT    NOT NULL, 
     PRIMARY KEY(courseID) 
    ); 

    -- HOLDS A SPECIFIC COURSE OFFERINGS -- 
    CREATE TABLE ClassesAvailable (
     courseID INT NOT NULL, 
     year  INT NOT NULL, 
     term  TEXT NOT NULL, 
     CHECK(term = 'Fall' OR term = 'Winter' OR term = 'Spring' OR term = 'Summer'), 
     PRIMARY KEY(courseID, year, term) 
    ); 

    -- PEOPLE SUPERTYPE -- 
    CREATE TABLE People (
     pid SERIAL   UNIQUE NOT NULL, 
     fname TEXT      NOT NULL, 
     lname TEXT      NOT NULL, 
     PRIMARY KEY(pid) 
    ); 

    -- HOLDS THE DIFFERENT PROFESSORS TEACHING AT THE SCHOOL -- 
    -- SUBTYPE OF PEOPLE -- 
    CREATE TABLE Professors (
     professorID INT UNIQUE NOT NULL, 
     status  TEXT  NOT NULL, 
     CHECK(status = 'Full-Time' OR status = 'Part-time'), 
     PRIMARY KEY(professorID), 
     FOREIGN KEY(professorID) REFERENCES People(pid) 
    ); 

    -- HOLDS THE SPECIFIC INSTANCES OF THE CLASS DEPENDING ON THE YEAR AND TERM -- 
    CREATE TABLE Sections (
     courseID  INT   NOT NULL, 
     year   INT   NOT NULL, 
     term   TEXT   NOT NULL, 
     sectionNumber INT   NOT NULL, 
     startDate  DATE   NOT NULL, 
     endDate  DATE   NOT NULL, 
     crn   INT   NOT NULL, 
     classSize  INT   NOT NULL, 
     CHECK(term = 'Fall' OR term = 'Winter' OR term = 'Spring' OR term = 'Summer'), 
     PRIMARY KEY(courseID, year, term, sectionNumber), 
     FOREIGN KEY(courseID, year, term) REFERENCES ClassesAvailable(courseID, year, term) 
    ); 

    -- HOLDS THE EVENT OF THE CLASS -- 
    -- A CLASS MAY HAVE DIFFERENT DAYS ON WHICH -- 
    -- THEY MEET ON, SO THIS ALLOWS A CERTAIN -- 
    -- SECTION TO HAVE SEVERAL DAYS WITHOUT CONFLICT -- 
    CREATE TABLE ClassEvent (
     professorID INT   NOT NULL, 
     courseID  INT   NOT NULL, 
     year   INT   NOT NULL, 
     term   TEXT   NOT NULL, 
     sectionNumber INT   NOT NULL, 
     day   TEXT, 
     startTime  TIME, 
     endTime  TIME, 
     location  TEXT, 
     campus  TEXT, 
     CHECK(day = 'Monday' OR day = 'Tuesday' OR day = 'Wednesday' OR day = 'Thursday' OR day = 'Friday' OR day = 'Saturday' OR day = 'Sunday' OR day IS NULL), 
     CHECK(term = 'Fall' OR term = 'Winter' OR term = 'Spring' OR term = 'Summer'), 
     CHECK(campus = 'Main' OR campus = 'Online' OR campus = 'Italy'), 
     PRIMARY KEY(professorID, courseID, year, term, sectionNumber, day, startTime, endTime), 
     FOREIGN KEY(professorID) REFERENCES Professors(professorID), 
     FOREIGN KEY(courseID, year, term, sectionNumber) REFERENCES Sections(courseID, year, term, sectionNumber) 
    ); 

    -- GENERATES THE PREREQUESITES -- 
    CREATE TABLE Prerequisites (
     courseID  INT  NOT NULL, 
     year   INT  NOT NULL, 
     term   TEXT  NOT NULL, 
     prereqID  INT  NOT NULL, 
     CHECK(term = 'Fall' OR term = 'Winter' OR term = 'Spring' OR term = 'Summer'), 
     PRIMARY KEY(courseID, year, term, prereqID), 
     FOREIGN KEY(courseID, year, term) REFERENCES ClassesAvailable(courseID, year, term), 
     FOREIGN KEY(prereqID) REFERENCES Courses(courseID) 
    ); 


    -- HOLDS THE STUDENTS THAT WILL BE TAKING THE CLASSES -- 
    -- SUBTYPE OF PEOPLE -- 
    CREATE TABLE Students (
     studentID  INT UNIQUE NOT NULL, 
     gradYear  INT   NOT NULL, 
     creditsEarned INT   NOT NULL, 
     PRIMARY KEY(studentID), 
     FOREIGN KEY(studentID) REFERENCES People(pid) 
    ); 

    -- HOLDS A CLASS RECORD FOR STUDENTS (AND POSSIBLY PROFESSORS) -- 
    CREATE TABLE Enrollment (
     studentID  INT   NOT NULL, 
     courseID  INT   NOT NULL, 
     year   INT   NOT NULL, 
     term   TEXT  NOT NULL, 
     sectionNumber INT   NOT NULL, 
     CHECK(term = 'Fall' OR term = 'Winter' OR term = 'Spring' OR term = 'Summer'), 
     PRIMARY KEY(studentID, courseID, year, term, sectionNumber), 
     FOREIGN KEY(studentID) REFERENCES Students(studentID), 
     FOREIGN KEY(courseID, year, term, sectionNumber) REFERENCES Sections(courseID, year, term, sectionNumber) 
    ); 

    -- HOLDS THE DIFFERENT DEGREES THAT CAN BE ATTAINED AT THE COLLEGE/UNIVERSITY -- 
    CREATE TABLE Degrees (
     degreeID  SERIAL  UNIQUE NOT NULL, 
     degreeName TEXT    NOT NULL, 
     degreeType TEXT    NOT NULL, 
     degDepartment VARCHAR(4)   NOT NULL, 
     CHECK(degreeType = 'Major' OR degreeType = 'Minor' OR degreeType = 'Masters'), 
     PRIMARY KEY(degreeID) 
    ); 

    -- HOLDS THE CLASSES THAT WILL MAKE UP A DEGREE -- 
    CREATE TABLE DegreeReq (
     degreeID INT REFERENCES Degrees(degreeID) NOT NULL, 
     courseID INT REFERENCES Courses(courseID) NOT NULL, 
     PRIMARY KEY(degreeID, courseID) 
    ); 

    -- HOLDS THE INSTANCE OF A DEGREE FOR A CERTAIN STUDENT -- 
    -- FOR EXAMPLE: A STUDENT CAN HAVE A MAJOR AND A MINOR -- 
    -- SO HE/SHE CAN STORE THEM SEPARATELY -- 
    CREATE TABLE DegreeInstance (
     degreeID  INT REFERENCES Degrees(degreeID) UNIQUE NOT NULL, 
     studentID  INT REFERENCES Students(studentID) UNIQUE NOT NULL, 
     startDate  DATE          NOT NULL, 
     endDate   DATE          NOT NULL, 
     creditsRequired INT          NOT NULL, 
     PRIMARY KEY(degreeID, studentID) 
    ); 

    -- HOLDS ALL THE RATE MY PROFESSOR STATS -- 
    CREATE TABLE Rating (
     professorID  INT  UNIQUE NOT NULL, 
     rmpID   BIGINT  UNIQUE NOT NULL, 
     avgRating  FLOAT    NOT NULL, 
     avgHelpfulness FLOAT    NOT NULL, 
     avgClarity  FLOAT    NOT NULL, 
     avgEasiness  FLOAT    NOT NULL, 
     PRIMARY KEY(professorID, rmpID), 
     FOREIGN KEY(professorID) REFERENCES Professors(professorID) 
    ); 

    -- HOLDS CLASS RECORDS FOR STUDENTS -- 
    CREATE TABLE ClassRecord (
     studentID INT NOT NULL, 
     courseID INT NOT NULL, 
     year  INT NOT NULL, 
     term  TEXT NOT NULL, 
     grade  TEXT NOT NULL, 
     CHECK(grade = 'A' OR grade = 'A-' OR grade = 'B+' OR grade = 'B' OR grade = 'B-' OR grade = 'C+' OR grade = 'C' OR grade = 'C-' OR grade = 'D+' OR grade = 'D' OR grade = 'D-' OR grade = 'F' OR grade = 'P'), 
     PRIMARY KEY(studentID, courseID, year, term, grade), 
     FOREIGN KEY(courseID, year, term) REFERENCES ClassesAvailable(courseID, year, term), 
     FOREIGN KEY(studentID) REFERENCES Students(studentID) 
    ); 

Answer 1

我知道的2個選項，可以幫助您的快照。您可以使用DISTINCT或GROUP BY。

DISTINCT會是什麼樣子：

SELECT DISTINCT c.courseName, l.day, l.startTime, l.endTime 

這可以確保唯一行返回。

的GROUP BY選項看起來像：

AND l.sectionNumber = e.sectionNumber) 
GROUP BY c.courseName, l.day, l.startTime, l.endTime 
ORDER BY 

這也將確保返回僅1行中的每樣組。

使用DISTINCT您可以輕鬆添加更多選擇列而無需進行其他更改。 DISTINCT將確保整行的列是不同的。

對於GROUP BY，每次更改選擇列時，還需要更新GROUP BY子句。

從性能角度來看，GROUP BY在處理多列時傾向於首選。當獲得單個列的所有不同值時，DISTINCT似乎更常見。