语法有什么问题？

Question

CREATE TABLE Existing_medical_condition (
    condition VARCHAR(50) NOT NULL, 
    date_of_diagnosis DATE, treatment TEXT, 
    pssn INT NOT NULL, 
    CONSTRAINT emc_key PRIMARY KEY(condition, pssn), 
    FOREIGN KEY(pssn) REFERENCES Patient(ssn) 
); 

给出错误：

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'condition VARCHAR(50) NOT NULL, date_of_diagnosis DATE, treatment TEXT, pssn INT' at line 1

Answer 1

条件是reserved word。您必须将其包含在反引号中：

CREATE TABLE Existing_medical_condition (
    `condition` VARCHAR(50) NOT NULL, 
    date_of_diagnosis DATE, 
    treatment TEXT, 
    pssn INT NOT NULL, 
    CONSTRAINT emc_key 
    PRIMARY KEY(condition, pssn), 
    FOREIGN KEY(pssn) REFERENCES Patient(ssn)); 

Answer 2

尽量避免为列名保留关键字。如果你还想要，你可以在下面写。

CREATE TABLE Existing_medical_condition ([condition] VARCHAR(50) NOT NULL,  date_of_diagnosis DATE, treatment TEXT, 
pssn INT NOT NULL, CONSTRAINT emc_key PRIMARY KEY(condition, pssn), FOREIGN KEY(pssn)  REFERENCES Patient(ssn));