Question

I’m trying to run a query, that I will turn into a mySQL query from a from with multiple search options. Here’s the query I’m testing in myPHPadmin

SELECT Fname, Minit, Lname, Address, Hourly, Sname, Saddress, Dno
FROM (SELECT * 
FROM EMPLOYEE, DEPARTMENT, LOCATION
WHERE EMPLOYEE.Dno = DEPARTMENT.Dnumber AND
LOCATION.Store_num = DEPARTMENT.Store_num AND
(Fname='100' OR Lname='100' 
OR LOCATION.Store_num ='100' OR Dno='100')) X

All of the OR statements will turn into ‘?’ in mySQL, so for now I’m using 100 which will only work with Store_num. So this should bring up a list of the employees who work at that store.

However, the error I’m getting says: #1060 – Duplicate column name ‘Mgr_ssn’

Here are my tables, not sure why they aren’t merging correctly.

CREATE TABLE EMPLOYEE
(   Fname       VARCHAR(15) not null,
    Minit       CHAR,
    Lname       VARCHAR(15) not null,
    Ssn         CHAR(9)     not null,
    Bdate       DATE,
    Address     VARCHAR(30), 
    Hourly      DECIMAL(5,2), 
    Mgr_ssn     CHAR(9),
    Dno         INT     not null,
    Start_date  DATE,
    Phone       CHAR(10),   
    PRIMARY KEY (Ssn),
    FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE(Ssn), 
    FOREIGN KEY (Dno) REFERENCES DEPARTMENT(Dnumber) );

CREATE TABLE DEPARTMENT
(   Dname       VARCHAR(15) not null,
    Dnumber     INT         not null,
    Mgr_ssn     CHAR(9)     not null,
    Mgr_start_date  DATE,
    Phone       CHAR(10),
    Store_num   INT     not null,
    PRIMARY KEY (Dnumber, Store_num),
    UNIQUE (Dname),
    FOREIGN KEY (Mgr_ssn) REFERENCES EMPLOYEE(Ssn),
    FOREIGN KEY (Store_num) REFERENCES LOCATION(Store_num) 
);

CREATE TABLE LOCATION
(   Store_num   INT         NOT NULL,
    Sname       VARCHAR(15)     NOT NULL, 
    Saddress    VARCHAR(30) NOT NULL,
    PRIMARY KEY (Store_num), 
    UNIQUE (Saddress)
);

Answer 1

the problem is here

SELECT *  FROM EMPLOYEE, DEPARTMENT, LOCATION

tables EMPLOYEE and DEPARTMENT have both Mgr_ssn column. you need to specify the table in which Mgr_ssn come from, ex

SELECT EMPLOYEE.Mgr_ssn AS `EMP_Mgr_ssn`,
       DEPARTMENT.Mgr_ssn AS `DEP_Mgr_ssn`,
       .....
FROM EMPLOYEE, DEPARTMENT, LOCATION

an alias would also help you solve it.

so the full query would be

SELECT Fname, Minit, Lname, Address, Hourly, Sname, Saddress, Dno
FROM 
(
    SELECT LOCATION.*,
           Employee.Mgr_ssn AS `EMP_Mgr_ssn`,
           DEPARTMENT.Mgr_ssn AS `DEP_Mgr_ssn`,
           Employee.Fname,
           Employee.Minit,
           Employee.Lname,
           Employee.Address,
           Employee.Hourly,Employee.Dno
    FROM EMPLOYEE, DEPARTMENT, LOCATION
    WHERE EMPLOYEE.Dno = DEPARTMENT.Dnumber AND
          LOCATION.Store_num = DEPARTMENT.Store_num AND
        (Fname='100' OR Lname='100' 
         OR LOCATION.Store_num ='100' OR Dno='100'
        )
) X

but this query will also work because you don’t Mgr_ssn column

SELECT Fname, Minit, Lname, Address, Hourly, Sname, Saddress, Dno
FROM 
(
    SELECT LOCATION.*,
           Employee.Fname,
           Employee.Minit,
           Employee.Lname,
           Employee.Address,
           Employee.Hourly,Employee.Dno
    FROM EMPLOYEE, DEPARTMENT, LOCATION
    WHERE EMPLOYEE.Dno = DEPARTMENT.Dnumber AND
          LOCATION.Store_num = DEPARTMENT.Store_num AND
        (Fname='100' OR Lname='100' 
         OR LOCATION.Store_num ='100' OR Dno='100'
        )
) X

• SQLFiddle Demo