字段列表中的“SSN”列不明确

Question

I have three tables viz- Student,Enrolls and Course. I wanted to fetch the information about students (their SSN,First and Last Names) who took course as Computer Architecture.

I wrote a query like

select SSN,First_Name,Last_Name,Course_Name='Computer Architecture'
from STUDENT s,ENROLLS e,COURSE c where s.SSN=e.SSN and e.CourseNo=c.CourseNo;

and got an error saying:

ERROR 1052 (23000): Column 'SSN' in field list is ambiguous

My table structure is as follows

Student(SSN,First_Name,Last_Name,Street,City,Zip,State)
Course(CourseNo,Course_Name,Department)
Enrolls(SSN,SectionNo,CourseNo)

Where am I getting it wrong?

Answer 1

You add simply the alias name in forint of it and so it becomes unambiguously

I also changed it to JOINs, your method is since many years outdated

SELECT 
    e.SSN,
    First_Name,
    Last_Name,
    Course_Name = 'Computer Architecture'
FROM
    STUDENT s
    INNER JOIN 
    ENROLLS e ON s.SSN = e.SSN
    INNER JOIN
    COURSE c ON e.CourseNo = c.CourseNo;

Answer 2

SQL supports qualifying a column by prefixing the reference with either the full table name or table alias:

SELECT 
    e.SSN,
    First_Name,
    Last_Name,
    Course_Name = 'Computer Architecture'
FROM STUDENT s
    JOIN 
    ENROLLS e ON s.SSN = e.SSN
    JOIN
    COURSE c ON e.CourseNo = c.CourseNo;