Is it possible to specify which is the primary key on creating table as select statement? My aim is to include the declaration of primary key on the create table not modifying the table after the creation.
CREATE TABLE suppliers
AS (SELECT company_id, address, city, state, zip
FROM companies
WHERE company_id < 5000);
Yes, it's possible. You would need to specify columns explicitly:
CREATE TABLE suppliers (
company_id primary key,
address,
city,
state,
zip
)
AS
SELECT company_id, address, city, state, zip
FROM companies
WHERE company_id < 5000;
Here is a demo
Note: in this case primary key constraint will be given a system-generated name. If you want it to have a custom name you'd have to execute alter table suppliers add constraint <<custom constraint name>> primary key(<<primary_key_column_name>>) after executing(without primary key specified) CREATE TABLE suppliers.. DDL statement.
Yes, it's possible.You can try referring below example.
create table student (rollno ,student_name,score , constraint pk_student primary key(rollno,student_name))
as
select empno,ename,sal
from emp;
You can create Suppliers table explicitly and if any column have primary key in companies table, then copy that structure from companies table.
Or
Create a same column defining primary key that you want and copy that column from companies table!
Related
CREATE TABLE Route(
RouteNo VARCHAR(10),
Origin VARCHAR(30),
Destination VARCHAR(30),
DepartureTime VARCHAR(15),
SerialNo VARCHAR(5),
ArrivalTime VARCHAR(15),
PRIMARY KEY(RouteNo) );
CREATE TABLE Employee(
EmployeeID VARCHAR(5) NOT NULL,
Name VARCHAR(30),
Phone NUMBER,
JobTitle VARCHAR(30),
PRIMARY KEY(EmployeeID) );
CREATE TABLE Flight(
SerialNo VARCHAR(5),
RouteNo VARCHAR(5),
FlightDate DATE,
ActualTD VARCHAR(10),
ActualTA VARCHAR(10),
PRIMARY KEY(SerialNo, RouteNo, FlightDate),
FOREIGN KEY(RouteNo) REFERENCES Route(RouteNo),
FOREIGN KEY(SerialNo) REFERENCES Airplane(SerialNo) ); -- does Airplane table exists ?
CREATE TABLE CrewAssigment(
EmployeeID VARCHAR(5),
RouteNo VARCHAR(5),
FlightDate DATE,
Role VARCHAR(45),
Hours INT,
PRIMARY KEY(EmployeeID, RouteNo, FlightDate),
FOREIGN KEY(EmployeeID) REFERENCES Employee(EmployeeID),
FOREIGN KEY(RouteNo) REFERENCES Route(RouteNo),
FOREIGN KEY(FlightDate) REFERENCES Flight(FlightDate) );
Select * from CrewAssignment
This is my code where I'm getting an error in the CrewAssignment table and above are the tables where the foreign key is referenced from.
Error report -
ORA-02270: no matching unique or primary key for this column-list
02270. 00000 - "no matching unique or primary key for this column-list"
*Cause: A REFERENCES clause in a CREATE/ALTER TABLE statement
gives a column-list for which there is no matching unique or primary
key constraint in the referenced table.
*Action: Find the correct column names using the ALL_CONS_COLUMNS
catalog view
A few objections.
This is clearly an Oracle question, not MySQL. How do I know? ORA-02270 is an Oracle database error code; pay attention to tags you use.
You should use VARCHAR2 datatype instead of VARCHAR. Why? Oracle recommends so.
create table flight fails first as it references the airplane table, and it doesn't exist yet (at least, not in code you posted)
error you're complaining about is due to create table crewassignment. One of its foreign keys references the flight table:
FOREIGN KEY(flightdate) REFERENCES flight(flightdate)
but flight's primary key is composite, made up of 3 columns:
PRIMARY KEY(serialno,
routeno,
flightdate)
which means that you can't create that foreign key.
So, what to do? No idea, I don't know rules responsible for such a data model. Either modify primary key of the flight table, or modify foreign key constraint of the crewassingment table.
Perhaps you could add a new column to flight table (made up of a sequence (or identity column, if your database version supports it) and then let the crewassignment table reference that primary key. Columns you currently use as a primary key (serialno, routeno, flightdate) would then switch to unique key.
ORDERS table in the Oracle Database:
ORDERS
ORDER_ID NOT NULL NUMBER(4)
ORDATE_DATE DATE
CUSTOMER_ID NUMBER(3)
ORDER_TOTAL NUMBER(7,2)
The ORDERS table contains data and all orders have been assigned a customer ID. I'm trying to add a NOT NULL constraint to the CUSTOMER_ID column. Would I use MODIFY CONSTRAINT or ADD CONSTRAINT? I was told you have to drop the constraint and ADD the new one, but if there is no existing constraint to Customer ID number, would it be MODIFY?
alter table orders modify customer_id not null;
Just MODIFY the column:
alter table orders modify customer_id not null;
Alternatively, you could add an [overkill] constraint in the form:
alter table orders add constraint nn1 check (customer_id is not null);
Just use the first form.
As a side note, some databases (such as Oracle) consider those two constraint different and somewhat separate: the former is a column constraint, while the latter is a table constraint. Oracle keeps track in case you drop one, while the other is still in effect.
currently i am facing an oracle constraints issue.
After submiting an insert my foreign key constraint(s) won't fire. What it should do is giving two tables the same ID, but unfortunately only the one table with the primary Key is giving an ID. The column with the foreign key in the second table remains null.
For Instance: Insert into table t1 (t1_id,name, dpt) values (value1 (trigger with autoincrement for id), value2, value3); The same procedure is behind table 2, table 3 ... All constraints are written correctly
Table 1 (Emp)
ID Name Department
1 Joe HR
Table 2 (Projects)
ID Project EmpID
1 new (null) -> must be 1
Thank you in advanced.
Constraint: ALTER TABLE "PROJECTS" ADD CONSTRAINT "EMP_FK" FOREIGN KEY ("EMP_ID")
REFERENCES "EMP" ("EMP_ID") ON DELETE CASCADE ENABLE
Trigger: create or replace TRIGGER Projects_TRG BEFORE
INSERT ON Projects FOR EACH ROW BEGIN :NEW.Project_ID := Projects_SEQ.NEXTVAL;
END;
How do i manage to populate the parent id from the parent table into the child table?
Please note that I used different names in my application.
It appears that you've misunderstood the purpose of a foreign key constraint. A foreign key constraint does NOT automatically propagate constraint values from the parent table to the child table. The purpose of the constraint is to ensure that the values of the key column in the child table, when populated, have matching values in the key column of the parent table. Your application is responsible for ensuring that the key column on the child table is populated with the appropriate value. The constraint doesn't do that for you. It's also perfectly legitimate to have a NULL in the key column of the child table, assuming the the column on the child table doesn't have a NOT NULL constraint on it.
I have 4 tables
customer: CustomerID - primary key, name
Magazine: name - primary key, cost, noofissues
Newspaper: name - primary key, cost, noofissues
subscription: custID - references CustomerID of Customer, name, startdate, enddate
In the above, can I reference the name from subscription table to reference name from Magazine and name from Newspaper?
I have created the tables Customer, Newspaper and Magazine. I only need to create Subscription.
Can you do something like this?
CREATE TABLE subscription (
custID INT
CONSTRAINT subscription__custid__fk REFERENCES Customer( CustomerId ),
name VARCHAR2(50)
CONSTRAINT subscription__mag_name__fk REFERENCES Magazine( Name )
CONSTRAINT subscription__news_name__fk REFERENCES Newspaper( Name ),
startdate DATE
CONSTRAINT subscription__startdate__nn NOT NULL,
enddate DATE
);
Yes, you can and you will have two foreign keys on the same column pointing to different tables but if the value in the column is non-null then it will expect there to be a matching name in both the magazines table and the newspapers table - which is probably not what you are after.
Can you have a foreign key that asks can the value be in either exclusively in this table or that table (but not in both)? No.
But you can re-factor your database so you merge the newspapers and magazines tables into a single table (which you can then easily reference); like this:
CREATE TABLE customer (
CustomerID INT
CONSTRAINT customer__CustomerId__pk PRIMARY KEY,
name VARCHAR2(50)
CONSTRAINT customer__name__nn NOT NULL
);
CREATE TABLE Publications (
id INT
CONSTRAINT publications__id__pk PRIMARY KEY,
name VARCHAR2(50)
CONSTRAINT publications__name__nn NOT NULL,
cost NUMBER(6,2)
CONSTRAINT publications__cost__chk CHECK ( cost >= 0 ),
noofissues INT,
type CHAR(1),
CONSTRAINT publications__type__chk CHECK ( type IN ( 'M', 'N' ) )
);
CREATE TABLE subscription (
custID INT
CONSTRAINT subscription__custid__fk REFERENCES Customer( CustomerId ),
pubID INT
CONSTRAINT subscription__pubid__fk REFERENCES Publications( Id ),
startdate DATE
CONSTRAINT subscription__startdate__nn NOT NULL,
enddate DATE
);
If you are asking whether you can create a foreign key constraint on subscription that references either the newspaper table or the magazine table, the answer is no, you cannot. A foreign key must reference exactly one primary key.
Since magazine and newspaper have the same set of attributes, the simple option is to combine them into a single periodical table with an additional periodical_type column to indicate whether it is a magazine or a newspaper. You could then create your foreign key to the periodical table.
Although it probably won't make sense in this particular example, you could also have separate columns in subscription for magazine_name and newspaper_name and create separate foreign key constraints on those columns along with a check constraint that ensured that exactly one of the values was non-NULL. That might make sense if the two different parent tables had radically different attributes.
Not related to your question but as a general bit of advice, I wouldn't use the name as the primary key. In addition to being rather long, names tend to change over time and names aren't necessarily unique. I would use a different attribute for the key, potentially a synthetic primary key generated from a sequence.
I have a table STUDENT with columns st_id,name,age,dept_name. Now I want to create a new table STUDENT_DESC with columns st_id,dept_name,st_desc. So I need to copy all the values of st_id and dept_name to the newly created table STUDENT_DESC. I need to ensure relationship while copying st_id and dept_name , the dept_name should be corresponding to st_id.So how can I do it in PL/SQL?
insert into STUDENT_DESC (select st_id, dept_name, null from student);
this will simply copy all the records. The third column st_desc is left empty (null)
To ensure referential integrity you would add a primary key and a referential integrity constraint to the STUDENT_DESC table
However, note that in many cases it could be "wrong" to introduce a second table containing student data like that. It could be "better" to add st_desc to the STUDENT table.
I'm not sure I understand your data model, but at face value you can create your table simply:
CREATE TABLE student_desc AS SELECT st_id, dept_name FROM student;
ALTER TABLE student_desc ADD (st_desc VARCHAR2(..));
Fill in the .. with the desired max size for st_desc.