Here is my main table:
create table employee
(
eno SERIAL primary key,
ename varchar(100) not null,
title varchar(100) not null
);
I want to referenced the title only because I've already referenced the eno in another table.
create table pay
(
title varchar(100),
sal money not null,
foreign key(title) references employee(title)
);
I get an error that there is no unique constraint matching given keys for referenced table "employee" 1
Please help me. I'm having a hard time solving this error. I'm still a beginner at SQL. thanks a lot
There is no limit to the number of tables that may reference a given table.
Foreign keys may only reference primary keys.
Use a foreign key to eno:
create table pay
(
eno varchar(100),
sal money not null,
foreign key(eno) references employee(eno)
);
Related
I'm trying to write a script in Apex to create multiple tables. The first table is created with no issues but every table after that one gives me a missing parenthesis issue. Sometimes it's the left, sometimes it's the right. I've tried everything with no avail.
I have debugged it numerous times, spoken with the others and have not found the solution.
Create Table Employee -- Creates Employee table and references it to ProjDept table
(
EmployeeID Number(4) Not Null,
FirstName VarChar2(15) Not Null,
LastName VarChar2(20) Not Null,
ProjDeptID Number(4) Not Null,
PhoneNumber Number(10),
Constraint Employee_pk Primary Key (EmployeeID), -- sets primary key for table
Constraint Employee_FK Foreign Key References ProjDept(ProjDeptID)-- identifies foreign key
);
This is the second table in the script that won't work, the next 2 tables generate similar errors.
You forgot to include the name of the column which is referencing another in the foreign key:
Create Table Employee (
EmployeeID Number(4) Not Null,
FirstName VarChar2(15) Not Null,
LastName VarChar2(20) Not Null,
ProjDeptID Number(4) Not Null,
PhoneNumber Number(10),
Constraint Employee_pk Primary Key (EmployeeID), -- sets primary key for table
Constraint Employee_FK Foreign Key (ProjDeptId) References ProjDept(ProjDeptID)-- identifies foreign key
);
db<>fiddle
Where exactly in Apex are you executing those commands?
If SQL Workshop's SQL Commands, then you can't have more than a single command in there, i.e. you should create tables one by one:
create the first table
delete that create table command and write another one, for the second table; then create it
the same goes for other tables as well
Alternatively, go to SQL Workshop's SQL Scripts and put all your commands into a script, e.g.
create table a (id number, name varchar2(20), ...);
create table b (cdate date, ...);
save & run the script.
'''
CREATE TABLE Employee
(
employeeID INT (10) PRIMARY KEY,
Name CHAR (20)
);
'''
'''
CREATE TABLE SALARY
(
employeeID INT (10) PRIMARY KEY,
Salary INT (10)
);
'''
Is it possible to use the same primary key in both tables?
Yes. You can have same column name as primary key in multiple tables.
Column names should be unique within a table. A table can have only one primary key, as it defines the Entity integrity.
If this question is about data modelling parent-child relationship, There are two types. You are read more on this.
Identifying relationship : Child identifies itself by the help of parent. Here, Employee & Salary will share the same primary key. Primary key of parent table (EmployeeId) will be primary key of child table also (Salary).
Non-Identifying relationship: Child is having its own identity. Here, Employee & Salary will have different primary key. Child table will have its own primary key(say SalaryId) and will have primary key of parent as a Foreign key(EmployeeId).
If your question is if you can use the same EMPLOYEEID column as the primary ID on multiple tables, the answer is "YES, YOU CAN"
You can use the same column as primary index on multiple tables, but you cannot have more than one primary index on a table
Yes, you can. You would make salary.employeeid both the table's primary key and a foreign key to the employee table:
CREATE TABLE salary
(
employeeid INT (10) NOT NULL,
salary INT (10) NOT NULL,
CONSTRAINT pk_salary PRIMARY KEY (employeeid,
CONSTRAINT fk_salary_employeeid FOREIGN KEY (employeeid) REFERENCES employee (employeeid)
);
This creates a {1}:{0,1} relationship between the tables and ensures that you cannot store a salary without having stored the employee and that you cannot store more than one salary for one employee.
This is something we rarely do. (We would rather make the salary a column in the employee table.) The only advantage of a separate salary table I see is that you can grant rights on the employee table but revoke them on the salary table, so as to make the salary table invisible to some database users.
You can do this, however, it is bad design.
I would suggest having the EmployeeId as the PK on the employee table and the EmployeeId as a Foreign Key on the Salary table, with the Salary table having it's own PK (most likely SalaryId).
Also the field [Name] I would personally steer clear of too, as "Name" is a reserved word in SQL.
CREATE TABLE dbo.Employee
(
EmployeeId BIGINT IDENTITY(1,1)
,EmployeeName VARCHAR(20) NOT NULL
,CONSTRAINT PK_Emp PRIMARY KEY (EmployeeId)
);
GO
CREATE TABLE dbo.Salary
(
SalaryId BIGINT IDENTITY(1,1)
,EmployeeId BIGINT NOT NULL
,Salary INT NOT NULL
,CONSTRAINT PK_Sal PRIMARY KEY (SalaryId)
,CONSTRAINT FK_EmpSal FOREIGN KEY (EmployeeId)
REFERENCES Employee(EmployeeId)
);
GO
All of that said, I think a little more thought into the db structure you should most likely end up with 3 tables. It is likely that many staff will have the same salary, lets say 5 employees are on 40,000 and 3 are on 50,000, etc.
You will end up storing the same Salary value multiple times.
A better way is to store that value once and have a third table that links an employee with a salary (in this case I have called it [Earnings]).
With this structure the salary of say 40,000 is stored 1 time in the db and you can link an employeeId to it multiple times.
CREATE TABLE dbo.Employee
(
Id BIGINT IDENTITY(1,1)
,EmployeeName VARCHAR(20) NOT NULL
,CONSTRAINT PK_Emp PRIMARY KEY (Id)
);
GO
CREATE TABLE dbo.Salary
(
Id BIGINT IDENTITY(1,1)
,Salary INT NOT NULL
,CONSTRAINT PK_Sal PRIMARY KEY (Id)
);
GO
CREATE TABLE dbo.Earnings
(
Id BIGINT IDENTITY(1,1)
,EmployeeId BIGINT NOT NULL
,SalaryId BIGINT NOT NULL
,CONSTRAINT PK_Ear PRIMARY KEY (Id)
,CONSTRAINT FK_EmpEar FOREIGN KEY (EmployeeId)
REFERENCES Employee(Id)
,CONSTRAINT FK_SalEar FOREIGN KEY (SalaryId)
REFERENCES Salary(Id)
);
GO
Technically, it is possible.
However, it is advisable to use Foreign key. This will:
-Avoid redundancy
-Help in maintaining db structure
-Improve readability
For this example, use:
CREATE TABLE Employee ( EmployeeID INT PRIMARY KEY, Name CHAR (20), Primary Key (EmployeeId) );
CREATE TABLE SALARY ( SalaryId INT , EmployeeID INT , Salary INT (10), Primary Key (SalaryId), Foreign Key (EmployeeId) REFERENCES Employee );
*An even better approach would be to add a constraint instead of just mentioning
[key names]
Like:
CREATE TABLE Employee(
EmployeeId INT,
Name CHAR(20)
)
ALTER TABLE Employee ADD CONSTRAINT PK_EmployeeId PRIMARY KEY
Can do by differents ways
I have a "Main" table named "Peoples" with "peopleId" as PK Identity
"Child" tables
"PeopleDocs" with "peopleId" PK
"PeopleImages" with "peopleId" PK
"PeopleKeys" with "peopleId" PK.
So, when i create one
record on "Peoples" i populate the "childs" with empty records to work
later.
This logic is about a federal law on my country and some people
informations has a life cicle and must be deleted if the life cicle
ends or the owner of the data demands. So we split the people
sensitive data on child tables to not lose all bussiness records,
refferences and log about that people.
Col1 as Primary key on both tables
SELECT
P.COL1,
P.COL2,
C.COL2,
C.COL3
FROM
TBL1 P, TBL2 C
WHERE
C.COL1 = P.COL1
Or using joins
SELECT
P.COL1,
P.COL2,
C.COL2,
C.COL3
FROM
TBL1 AS P
INNER JOIN
TBL2 AS C
ON
C.COL1 = P.COL1
What I am trying to do ?
I am trying to create two tables and at the same time i am trying to link them together using foreign and primary keys. However I successfully create my parent table ( Student with primary key ) but failed to create child table ( Attendence with foreign key ).
What is the problem ?
I get the following error while creating Attendence table:
ERROR at line 5: ORA-01748: only simple column names allowed here
My code:
Student table:
create table Student (
ST_ROLLNO NUMBER(6) constraint s_pk primary key,
ST_NAME VARCHAR(30) not null,
ST_ADDRESS varchar(35) not null
);
Attendence table:
create table Attendence (
ST_ROLLNO NUMBER(6),
ST_DATE VARCHAR(30) not null,
ST_PRESENT_ABSENT varchar(1) not null,
constraint f_pk Attendence.ST_ROLLNO foreign key references Student(ST_ROLLNO)
);
Your foreign key constraint syntax is wrong; it should be:
constraint f_pk foreign key (ST_ROLLNO) references Student(ST_ROLLNO)
You are preceding the FK column name with the table name, which is wrong in itself, but also have it in the wrong place.
create table Student (
ST_ROLLNO NUMBER(6) constraint s_pk primary key,
ST_NAME VARCHAR(30) not null,
ST_ADDRESS varchar(35) not null
);
Table STUDENT created.
create table Attendence (
ST_ROLLNO NUMBER(6),
ST_DATE VARCHAR(30) not null,
ST_PRESENT_ABSENT varchar(1) not null,
constraint f_pk foreign key (ST_ROLLNO) references Student(ST_ROLLNO)
);
Table ATTENDENCE created.
According to oracle documentation,
ORA ERR
ORA-01748 only simple column names allowed here
The following is the cause of this error:
This SQL statement does not allow a qualified column name, such as
username.table.column or table.column.
Action you can take to resolve this issue: Remove the qualifications
from the column and retry the operation.
In your case, you are trying to refer to the table name while defining a constraint -
Attendence.ST_ROLLNO - WRONG.
It must contain a simple name without the table name or schema name.
I'm having some difficulties with a database I'm creating for a summer camp, specifically with the PK and FK constraints. When I declare the FK constraint (e.g. FOREIGN KEY(PID) references Campers(CamperID)) I get an error running my code through pgAdmin (I'm using PostgreSQL). I understand that, for example, the Campers table is not yet created, and this is most likely part/all of the roadblock, however I feel like my FKs are still wrong somehow. To my understanding, a FK is a PK in another table -- but I feel like there is some redundancy or disconnect between my tables.
I've put the syntax for some of my CREATE statements below. I'm not sure if I'll get reprimanded for the quality of my (somewhat vague) question, but I feel a bit lost and would appreciate any help or advice. Thank you in advance!
DROP TABLE IF EXISTS People;
CREATE TABLE People (
PID VARCHAR(10) NOT NULL UNIQUE,
FName TEXT NOT NULL,
LName TEXT NOT NULL,
DOB DATE NOT NULL,
ArrivalDate DATE NOT NULL DEFAULT CURRENT_DATE,
DepartureDate DATE,
US_PhoneNum VARCHAR(11) NOT NULL,
StreetAddress VARCHAR(200) NOT NULL,
Sex GENDER NOT NULL,
ZIP VARCHAR(10) NOT NULL,
PRIMARY KEY(PID),
FOREIGN KEY(PID) REFERENCES Campers(CamperID),
FOREIGN KEY(PID) REFERENCES Counselors(CounselorID),
FOREIGN KEY(ZIP) REFERENCES Zip(ZIP)
);
DROP TABLE IF EXISTS Zip;
CREATE TABLE Zip (
ZIP VARCHAR(10) NOT NULL,
City TEXT NOT NULL,
State VARCHAR(2) NOT NULL,
PRIMARY KEY(ZIP)
);
DROP TABLE IF EXISTS Campers;
CREATE TABLE Campers (
CamperID VARCHAR(10) NOT NULL REFERENCES People(PID),
AgeGroup AGES NOT NULL,
CabinID VARCHAR(2) NOT NULL,
Bed BEDTYPES NOT NULL,
GroupID VARCHAR(3) NOT NULL,
PRIMARY KEY(CamperID),
FOREIGN KEY(CamperID) REFERENCES People(PID),
FOREIGN KEY(CabinID) REFERENCES Cabins(CabinID),
FOREIGN KEY(Bed) REFERENCES Beds(Bed),
FOREIGN KEY(GroupID) REFERENCES Groups(GroupID)
);
DROP TABLE IF EXISTS Counselors;
CREATE TABLE Counselors (
CounselorID VARCHAR(10) NOT NULL REFERENCES People(PID),
GroupID VARCHAR(3) NOT NULL,
CabinID VARCHAR(2) NOT NULL,
PRIMARY KEY(CounselorID),
FOREIGN KEY(GroupID) REFERENCES Groups(GroupID),
FOREIGN KEY(CabinID) REFERENCES Cabins(CabinID)
);
ERROR message for further clarification:
ERROR: relation "campers" does not exist
********** Error **********
ERROR: relation "campers" does not exist
SQL state: 42P01
There are more tables (obviously) which I can provide the create statements for, if needed.
You should really start here: Foreign key.
In the context of relational databases, a foreign key is a field (or
collection of fields) in one table that uniquely identifies a row of
another table.
What you are trying to do in your script is to create a circular link between People, Campers and Counselors. Having a Primary Key field also a Foreign Key mandates that IDs across all referenced tables are identical.
... and to create a Foreign Key the referenced table must already exist in the database. So you should start with the table that does not have any Foreign Keys and create tables that reference only those tables created previously. Alternatively you can create all tables without Foreign Keys and add them later, when all the tables are present.
... and to answer the question, Foreign Keys are never necessary, but they might help.
I am still a beginner in SQL and i'm facing an issue. hope you can help me.
I have a table called Department where it has an attribute DEPARTMENT_NO as its primary key.
CREATE TABLE DEPARTMENT(
DEPARTMENT_NO INT NOT NULL,
NAME VARCHAR(25) NOT NULL,
LOCATION CHAR(15),
PRIMARY KEY(DEPARTMENT_NO));
I have another table called Doctor where it has an attribute DNUM as a foreign key referring to DEPARTMENT_NO :
CREATE TABLE DOCTOR(
DOCTOR_ID CHAR(9) NOT NULL,
DNUM INT NOT NULL,
NAME VARCHAR(20) NOT NULL,
DOB DATE,
SPECIALTY VARCHAR(20) NOT NULL,
SALARY INT,
CITY VARCHAR(15),
STREET VARCHAR(15),
START_DATE DATE,
PRIMARY KEY(DOCTOR_ID))
FOREIGN KEY(DNUM) REFERENCES DEPARTMENT(DEPARTMENT_NO));
A doctor can be working in one or two departments. So, if I have a doctor working in department 1 and 4 (the values for DNUM will include 1 and 4).
I initially chose the data type of DNUM to be INT(same as DEPARTMENT_NO data type). But INT is not ideal for multiple values.
What should the data type be? or what other solution i have if,for example, I run a query for returning the name of the doctors working in department 4.
The query should return all the names of doctors working in department 4(only) and the ones who work in multiple departments(including 4).
Thanks very much in advance and sorry for the long message.
The standard way to represent a "many to many" relationship is via a "junction" (aka "link") table:
CREATE TABLE DOCTOR_DEPARTMENT (
DOCTOR_ID INT REFERENCES DOCTOR(DOCTOR_ID),
DEPARTMENT_NO INT REFERENCES DEPARTMENT (DEPARTMENT_NO),
PRIMARY KEY (DOCTOR_ID, DEPARTMENT_NO)
);
Note the key on {DOCTOR_ID, DEPARTMENT_NO}, which ensures the same doctor cannot be connected to the same department twice.
It also implicitly creates a composite (aka. "concatenated") index on these fields in that order, which makes it very quick to find departments of a given doctor (via an index range scan). If you need to query in the opposite "direction" (for doctors of the given department), flip the order of fields. If you need both queries, then you'll need both indexes (i.e. you'll need to create one index explicitly).
Consider adding ORGANIZATION INDEX clause, if you need just one of these indexes.
You need an additional table called doctor_department
create table doctor_department
(doctor_id integer references doctor(doctor_id) not null,
dnum integer references department(dnum) not null
)
You can create another table with relation to these 2 tables
Say,
Create table Dept_Doctors(
ID int not null,
DOCTOR_ID char(9) not null,
DEPARTMENT_NO INT NOT NULL,
PRIMARY KEY (ID),
FOREIGN KEY(DEPARTMENT_NO) REFERENCES DEPARTMENT(DEPARTMENT_NO),
FOREIGN KEY(DOCTOR_ID) REFERENCES DOCTOR(DOCTOR_ID));
You can join the 3 tables and get the desired result.