SQL查詢只返回一個結果/行而不是全部

Question

我有一個複雜的SQL查詢，這意味着返回所選擇的汽車給出的所有評論，但是，我只被顯示一個如下所示，而不是所有的他們喜歡截圖二。

這是我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"); 

這是我的複雜SQL查詢：

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 

這是我sqlfiddle：http://sqlfiddle.com/#!9/c9a92c/8

Answer 1

你缺少的子查詢中group by：

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; 

編輯：

如果你想評論和平均，你需要一個附加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;