mysql错误！是否可以在 mysql 中使用 table 变量？

Question

我正在学习 mysql 并且我正在测试分配 table 变量以从相同的 table 检索信息。我有一个简单的 table 学生，我想要一对具有相同 GPA 的学生（来自同一个 table -student-。所以我为学生 1 (S1) 和另一个分配了一个变量一个用于 S2，我希望成对的不同学生具有相同的 GPA，但我得到了其他东西；另一件事要提到的是，如果我将查询结果导出到 csv 文件，只有 S1 数据在 table、S2信息为空白（空单元格），变量在 mysql 中的工作方式是否不同？

这是 SQL 课程中的查询（我无法在 mysql 中复制）

SELECT s1.sID, s1.sName, s1.GPA, s2.sID, s2.sName, s2.GPA
FROM student s1, student s2
WHERE s1.GPA = s2.GPA AND s1.sID < s2.sID;

这里是 table 和数据：

--tables
CREATE TABLE college(
    cName VARCHAR(15),
    state VARCHAR(15),
    enrollment INT,
    PRIMARY KEY(cName)
);
CREATE TABLE student(
    sID INT,
    sName VARCHAR(40),
    GPA DECIMAL(3,1),
    sizeHS INT,
    PRIMARY KEY(sID)
);

CREATE TABLE application(
    sID INT,
    cName VARCHAR(20),
    major VARCHAR(20),
    decision VARCHAR(1),
    PRIMARY KEY(sID, cName, major)
);

--college data injection
INSERT INTO college VALUES('UNAM', 'Mexico City', 360000);
INSERT INTO college VALUES('UAM', 'Mexico City', 250000);
INSERT INTO college VALUES('Tec Culiacan', 'Sinaloa', 9000);
INSERT INTO college VALUES('UAS', 'Sinaloa', 110000);
INSERT INTO college VALUES('UACH', 'Chihuahua', 65000);
INSERT INTO college VALUES('Tec Monterrey', 'Nuevo Leon', 7500);

--student data injection
INSERT INTO student VALUES(9832, 'Juan Perez', 85.0, 3000);
INSERT INTO student VALUES(0219, 'Maria Gonzalez', 92.0, 9000);
INSERT INTO student VALUES(1683, 'Pedro Sanchez', 79.0, 13000);
INSERT INTO student VALUES(8329, 'Pilar Madrid', 83.0, 1500);
INSERT INTO student VALUES(0921, 'Eva Quintero', 80.0, 7900);
INSERT INTO student VALUES(9816, 'Francisco Hernandez', 96.0, 6500);

--application data injection
INSERT INTO application VALUES(9816, 'UNAM', 'CS', 'Y');
INSERT INTO application VALUES(9816, 'UAM', 'EE', 'Y');
INSERT INTO application VALUES(8329, 'Tec Monterrey', 'MGMT', 'N');
INSERT INTO application VALUES(8329, 'UNAM', 'Admin', 'N');
INSERT INTO application VALUES(1683, 'UAM', 'Biology', 'N');
INSERT INTO application VALUES(1683, 'UAS', 'Biology', 'Y');
INSERT INTO application VALUES(0219, 'Tec Culiacan', 'CS', 'Y');
INSERT INTO application VALUES(0219, 'UACH', 'CS', 'Y');
INSERT INTO application VALUES(0921, 'UAS', 'Industrial', 'Y');
INSERT INTO application VALUES(0921, 'Tec Culiacan', 'Mechatronic', 'N');
INSERT INTO application VALUES(9832, 'UAM', 'Arch', 'Y');
INSERT INTO application VALUES(0921, 'UACH', 'Industrial', 'N');

这是查询的预期结果：

Answer 1

您的查询工作正常，但首先确保您的学生在 Student table 中有相同的 GPA，然后再次运行查询。

--student data injection
INSERT INTO student VALUES(9832, 'Juan Perez', 85.0, 3000);
INSERT INTO student VALUES(0219, 'Maria Gonzalez', 92.0, 9000);
INSERT INTO student VALUES(1683, 'Pedro Sanchez', 96.0, 13000);
INSERT INTO student VALUES(8329, 'Pilar Madrid', 92.0, 1500);
INSERT INTO student VALUES(0921, 'Eva Quintero', 80.0, 7900);
INSERT INTO student VALUES(9816, 'Francisco Hernandez', 96.0, 6500);

运行查询的结果：

mysql错误！是否可以在 mysql 中使用 table 变量？

mysql error! Is it possible to use table variables in mysql?

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sql

variables

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