SQL查询仅返回一个结果/行，而不是全部

Question

I have a complex sql query which is meant to return all the reviews given by a selected car however, I am only being shown one as seen below as opposed to all of them like in screenshot two.

This is my DDL :

CREATE TABLE carsType(
    carsTypeID INTEGER NOT NULL AUTO_INCREMENT,
    carsTypeName VARCHAR(200) NOT NULL,
    PRIMARY KEY(carsTypeID)
);

CREATE TABLE carCategoryType(
    carCategoryTypeID INTEGER NOT NULL AUTO_INCREMENT,
    carCategoryTypeName VARCHAR(200) NOT NULL,
    PRIMARY KEY(carCategoryTypeID)
);

CREATE TABLE cars(
    carID INTEGER NOT NULL AUTO_INCREMENT,
    carsTypeID INTEGER NOT NULL,
    carCategoryTypeID INTEGER NOT NULL,
    carName VARCHAR(200),
    carArea VARCHAR(200),
    FOREIGN KEY(carsTypeID) REFERENCES carsType(carsTypeID),
    FOREIGN KEY(carCategoryTypeID) REFERENCES carCategoryType(carCategoryTypeID),
    PRIMARY KEY(carID)
);

CREATE TABLE carsReview(
    carID INTEGER NOT NULL,
    carMileage INTEGER NOT NULL,
    reviews VARCHAR(200) NOT NULL,
    FOREIGN KEY(carID) REFERENCES cars(carID)
);

INSERT INTO carsType VALUES
(NULL, "Hatchback"),
(NULL, "Saloon"),
(NULL, "Sedan");

INSERT INTO carCategoryType VALUES
(NULL, "A"),
(NULL, "B"),
(NULL, "C");

INSERT INTO cars VALUES
(NULL, 1, 1, "Golf", "Germany"),
(NULL, 2, 2, "Ford", "USA"),
(NULL, 2, 2, "Pontiac", "USA");

INSERT INTO carsReview VALUES
(1, 10000, "Good clean car"),
(2, 3000, "Worth it"),
(3, 1000, "Brand spanking new"),
(1, 45000, "She is good"),
(1, 100000, "Gone son"),
(1, 23000, "Looking fine");

This is my complex SQL query:

SELECT tbl_cars.carID, tbl_cars.carName, tbl_cars.carArea, 
        (IFNULL(tbl_carsReview.averageMileage, 0.0)) AS finalaverageMileage , tbl_carsReview.reviews, tbl_carsType.carsTypeName, 
        tbl_carCategoryType.carCategoryTypeName
        FROM cars tbl_cars
        INNER JOIN carsType tbl_carsType ON
        tbl_cars.carsTypeID = tbl_carsType.carsTypeID 
        INNER JOIN carCategoryType tbl_carCategoryType ON
        tbl_cars.carCategoryTypeID = tbl_carCategoryType.carCategoryTypeID
        LEFT JOIN (SELECT carsReview.carID, ROUND(AVG(carsReview.reviews),1) AS averageMileage, carsReview.reviews
        FROM carsReview) tbl_carsReview
        ON tbl_cars.carID = tbl_carsReview.carID 
        WHERE tbl_cars.carID = 1

This is my sqlfiddle : http://sqlfiddle.com/#!9/c9a92c/8

Answer 1

You are missing a group by in the subquery:

SELECT tbl_cars.carID, tbl_cars.carName, tbl_cars.carArea, 
       (IFNULL(tbl_carsReview.averageMileage, 0.0)) AS finalaverageMileage ,
       tbl_carsReview.reviews, tbl_carsType.carsTypeName, 
       tbl_carCategoryType.carCategoryTypeName
FROM cars tbl_cars INNER JOIN
     carsType tbl_carsType
     ON tbl_cars.carsTypeID = tbl_carsType.carsTypeID INNER JOIN
     carCategoryType tbl_carCategoryType
     ON tbl_cars.carCategoryTypeID = tbl_carCategoryType.carCategoryTypeID LEFT JOIN
     (SELECT carsReview.carID, ROUND(AVG(carsReview.reviews),1) AS averageMileage, carsReview.reviews
      FROM carsReview
      GROUP BY carsReview.carID
------^
     ) tbl_carsReview
     ON tbl_cars.carID = tbl_carsReview.carID 
WHERE tbl_cars.carID = 1;

EDIT:

If you want the reviews and the average, you need an additional join :

SELECT tbl_cars.carID, tbl_cars.carName, tbl_cars.carArea, 
       (IFNULL(tbl_carsReviewAvg.averageMileage, 0.0)) AS finalaverageMileage ,
       tbl_carsReview.reviews, tbl_carsType.carsTypeName, 
       tbl_carCategoryType.carCategoryTypeName
FROM cars tbl_cars INNER JOIN
     carsType tbl_carsType
     ON tbl_cars.carsTypeID = tbl_carsType.carsTypeID INNER JOIN
     carCategoryType tbl_carCategoryType
     ON tbl_cars.carCategoryTypeID = tbl_carCategoryType.carCategoryTypeID LEFT JOIN
     (SELECT carsReview.carID, ROUND(AVG(carsReview.reviews),1) AS averageMileage, carsReview.reviews
      FROM carsReview
      GROUP BY carsReview.carID
     ) tbl_carsReviewAvg
     ON tbl_cars.carID = tbl_carsReviewAvg.carID LEFT JOIN
     carsReview tbl_carsReview
     ON tbl_cars.carID = tbl_carsReview.carID
WHERE tbl_cars.carID = 1;