带有 JOINS 的 SQL SUM

Question

我正在尝试进行查询，以显示所有电影详细信息以及该电影售出的总票数。
这是我的桌子：
https://imgur.com/Tgu3XrA

到目前为止，这是我的代码：

SELECT Movies.MovieID, Title, Released, Runtime, Classification, 
SUM(Tickets.SessionID)
FROM Movies 
LEFT JOIN Sessions ON Movies.MovieID = Movies.MovieID 
LEFT JOIN Tickets ON Movies.MovieID = Tickets.SessionID
GROUP BY Movies.MovieID 
ORDER BY Released

结果如下： https://imgur.com/a/mRKYjNG

这是数据库的概要；

BEGIN TRANSACTION;
DROP TABLE IF EXISTS "Movies";
CREATE TABLE 'Movies' ('MovieID' INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 'Title' TEXT,'Released' INTEGER, 'Runtime' INTEGER,'Classification' TEXT, 'Plot' TEXT);
DROP TABLE IF EXISTS "Tickets";
CREATE TABLE 'Tickets' ('TicketID' INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 'SessionID' INTEGER,'PricePaid' REAL,'TimeStamp' INTEGER);
DROP TABLE IF EXISTS "MemberTickets";
CREATE TABLE 'MemberTickets' ('TicketID' INTEGER PRIMARY KEY NOT NULL,'MemberID' INTEGER,'OnlinePurchase' INTEGER);
DROP TABLE IF EXISTS "MovieGenre";
CREATE TABLE 'MovieGenre' ('MovieID' INTEGER NOT NULL, 'Genre' TEXT NOT NULL, PRIMARY KEY ('MovieID', 'Genre'));
DROP TABLE IF EXISTS "Sessions";
CREATE TABLE 'Sessions' ('SessionID' INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, 'MovieID' INTEGER,'SessionTime' INTEGER, 'NormalPrice' REAL, 'SeatsAvailable' INTEGER, 'RoomID' INTEGER);
DROP TABLE IF EXISTS "Members";
CREATE TABLE 'Members' ('MemberID' INTEGER primary key autoincrement ,FirstName TEXT, LastName TEXT, Postcode TEXT );
COMMIT;

Answer 1

您正在寻找COUNT()，而您的第二个JOIN 条件不正确。

SELECT m.MovieID, m.Title, m.Released, m.Runtime, m.Classification, 
       COUNT(t.SessionID)
FROM Movies m LEFT JOIN
     Sessions s
     ON s.MovieID = m.MovieID LEFT JOIN
     Tickets t
     ON t.SessionID = m.SessionID
GROUP BY m.MovieID, m.Title, m.Released, m.Runtime, m.Classification 
ORDER BY m.Released;

请注意，GROUP BY 包括 SQL 中的所有未聚合列。

请注意，我还包括了表别名并限定了所有列名。当查询具有多个表引用时，您应该始终限定所有列名。表别名使这更容易。