I have a very basic question regarding the Keys in SQL. I am trying to write an SQL statement so I can add the foreign key to my tables, however, it would always "table not found or missing". And the reason why I can't create that table is that the next table also has foreign keys from another table that I need to reference. Is there a way around it?
create table table_name (id char (3) primary key, name varchar (8));
SQL > table created.
create table table_name_2 (table2ID char (3) primary key, CID char (3),
name varchar (8), title varchar (8), foreign key (CID) references table_name_3);
SQL > missing table (table_name_3);
create table table_name_3 (CID char (3) primary key, tTitle varchar (8),
foreign key (phone) references table_name_4);
So I was only able to create table 3. What do I need to do so that I can create the table and add the foreign keys referencing while I write the SQL statements?
I am not ALLOWED to use ALTER table.
Create foreign keys separately, using the ALTER TABLE statement. Like this:
SQL> CREATE TABLE table_name(
2 id CHAR(3)PRIMARY KEY,
3 name VARCHAR(8)
4 );
Table created.
SQL> CREATE TABLE table_name_2(
2 table2id CHAR(3)PRIMARY KEY,
3 cid CHAR(3),
4 name VARCHAR(8),
5 title VARCHAR(8)
6 );
Table created.
SQL> CREATE TABLE table_name_3(
2 cid CHAR(3)PRIMARY KEY,
3 ttitle VARCHAR(8)
4 );
Table created.
Now the foreign key:
SQL> ALTER TABLE table_name_2 ADD CONSTRAINT fk_2_3 FOREIGN KEY(cid)
2 REFERENCES table_name_3;
Table altered.
SQL>
one approach you can od is to create the table with the Primary key and then do
and add the foreign key.
ALTER TABLE child_table
ADD CONSTRAINT fk_name
FOREIGN KEY (col1) REFERENCES parent_table(col1);
Related
CREATE TABLE report(
report_id NUMBER(5),
description VARCHAR2(200) NOT NULL,
status VARCHAR2(200) NOT NULL,
bicycle_id NUMBER(5),
cust_id NUMBER(5),
staff_id NUMBER(5),
CONSTRAINT ad_reportid_pk PRIMARY KEY (report_id),
CONSTRAINT ad_bicycle_fk FOREIGN KEY (bicycle_id) REFERENCES bicycle(bicycle_id),
CONSTRAINT ad_custid_fk FOREIGN KEY (cust_id) REFERENCES customer(cust_id),
CONSTRAINT ad_staffid_fk FOREIGN KEY (staff_id) REFERENCES staff(staff_id)
);
Above is the SQL script when I'm creating a table and it thrown me error with ORA-02264. I am neither drop the table nor creating that table. Tried to run this script
SELECT * FROM user_constraints WHERE CONSTRAINT_NAME = 'ad_bicycleid_fk'
and it showed no data.
All object names are stored in uppercase unless you mention it in double quotes while creating an object.
Try this:
SELECT * FROM user_constraints
WHERE upper(CONSTRAINT_NAME) = upper('ad_bicycleid_fk');
Here's an example which shows one option you might do that.
First, "dummy" tables which are being referenced by columns in the report table (why do I need them? Because create table report would fail otherwise):
SQL> create table bicycle
2 (bicycle_id number(5) constraint pk_bic primary key);
Table created.
SQL> create table customer
2 (cust_id number(5) constraint pk_cus primary key);
Table created.
SQL> create table staff
2 (staff_id number(5) constraint pk_sta primary key);
Table created.
The report table:
SQL> create table report
2 (report_id number(5),
3 description varchar2(200) not null,
4 status varchar2(200) not null,
5 bicycle_id number(5),
6 cust_id number(5),
7 staff_id number(5),
8 --
9 constraint pk_rep primary key (report_id),
10 constraint fk_rep_bic foreign key (bicycle_id)
11 references bicycle (bicycle_id),
12 constraint fk_rep_cus foreign key (cust_id)
13 references customer (cust_id),
14 constraint fk_rep_sta foreign key (staff_id)
15 references staff (staff_id)
16 );
Table created.
SQL>
Everything is OK.
Note the way I named constraints, especially foreign keys whose names show - at least approximately - which table references which another table, e.g. FK_REP_BIC - it is a Foreign Key from table REPort and it references the BICycle table. I'm not saying that you must do it that way, but - Google a little bit, read about good practices and find the one you prefer the most.
As of the constraint you couldn't find:
SQL> select owner, constraint_type, table_name
2 from user_constraints
3 where constraint_name = 'FK_REP_BIC';
OWNER C TABLE_NAME
--------------- - ---------------
SCOTT R REPORT
SQL>
CREATE TABLE "RESEARCH_DEP"."RESEARCH_TV_COMPANY"
( "CID" NUMBER(38,0) NOT NULL ENABLE,
"SOURCE_ID" NUMBER(2,0),
CONSTRAINT "PK_RESEARCH_TV_COMPANY_1" PRIMARY KEY ("CID", "SOURCE_ID")
USING INDEX (CREATE UNIQUE INDEX "RESEARCH_DEP"."IDX_TV_COMPANY_CID_SOURCE_ID" ON "RESEARCH_DEP"."RESEARCH_TV_COMPANY" ("CID", "SOURCE_ID")
CREATE TABLE "RESEARCH_DEP"."RESEARCH_METRICS_PHARMA_AUD"
( "ID" NUMBER GENERATED ALWAYS AS IDENTITY MINVALUE 1 MAXVALUE 9999999999999999999999999999 INCREMENT BY 1 START WITH 1 CACHE 20 NOORDER NOCYCLE NOKEEP NOSCALE NOT NULL ENABLE,
"SOURCE_ID" NUMBER(2,0) NOT NULL ENABLE,
"MEDIA_COMPANY_ID" NUMBER(*,0) NOT NULL ENABLE
)
NEED
ALTER TABLE RESEARCH_DEP.RESEARCH_METRICS_PHARMA_AUD
ADD CONSTRAINT fk_METRICS_PHARMA_AUD_TV_COMPANY_ID
FOREIGN KEY (MEDIA_COMPANY_ID,SOURCE_ID) REFERENCES RESEARCH_DEP.RESEARCH_TV_COMPANY(CID,SOURCE_ID);
ORA-02298: parent keys not found
DO I NEED TO CREATE A COMPOSITION COLUMN: CID,SOURCE_ID?
OR
create sequence of values two column oracle CID,SOURCE_ID ?
Your code is more or less OK:
SQL> create table research_tv_company
2 (cid number,
3 source_id number,
4 --
5 constraint pk_rtc primary key (cid, source_id)
6 );
Table created.
SQL> create table research_metrics_pharma_aud
2 (id number,
3 source_id number,
4 media_company_id number
5 );
Table created.
SQL> alter table research_metrics_pharma_aud
2 add constraint fk_rmpa_rtc
3 foreign key (media_company_id, source_id)
4 references research_tv_company (cid, source_id);
Table altered.
SQL>
Note that I
removed double quotes
removed NOT NULL for primary key columns (they can't be NULL anyway)
don't have any indexes created so Oracle will - along with table creation - create a primary key constraint AND unique index to support it
as I'm on 11gXE and it doesn't support identity columns, I removed that
from the second table; I'd have to enforce it via a trigger. You don't have to do anything about it, just saying (so that you wouldn't wonder where did it go?)
Error you got:
ORA-02298: parent keys not found
means that there are combinations of (media_company_id, source_id) in the second table that do not exist as pairs of (cid, source_id) in the first table. To illustrate it:
Drop the foreign key constraint first (otherwise, I wouldn't be able to do that):
SQL> alter table research_metrics_pharma_aud drop constraint fk_rmpa_rtc;
Table altered.
Insert a row into the first (master) table:
SQL> insert into research_tv_company (cid, source_id) values (1, 1);
1 row created.
Insert two rows into the second (detail) table; the first combination is valid, the second is not as (2, 2) don't exist in research_tv_company:
SQL> insert into research_metrics_pharma_aud (id, source_id, media_company_id) values (1, 1, 1);
1 row created.
SQL> insert into research_metrics_pharma_aud (id, source_id, media_company_id) values (2, 2, 2);
1 row created.
SQL>
If we try to create a foreign key constraint:
SQL> alter table research_metrics_pharma_aud
2 add constraint fk_rmpa_rtc
3 foreign key (media_company_id, source_id)
4 references research_tv_company (cid, source_id);
add constraint fk_rmpa_rtc
*
ERROR at line 2:
ORA-02298: cannot validate (SCOTT.FK_RMPA_RTC) - parent keys not found
SQL>
See? The same error you got.
What can you do?
insert missing primary key values into the master table, or
delete detail rows that violate the constraint, or
create the constraint, but instruct Oracle not to check whether existing rows are valid or not:
SQL> alter table research_metrics_pharma_aud
2 add constraint fk_rmpa_rtc
3 foreign key (media_company_id, source_id)
4 references research_tv_company (cid, source_id)
5 enable novalidate;
Table altered.
SQL>
The enable novalidate means that foreign key constraint will be enabled for any new or modified rows, but existing rows won't be checked. If that option suits you, use it. However, I believe that one of the first two option is better, with the first one - adding missing primary keys - being the best.
How can I inherit from two(or more) parent classes in ORACLE SQL? I've tried something like this:
ID(13),
OTHER_ID(9),
CONSTRAINT FK_ID FOREIGN
KEY(ID) REFERENCES TABLE_ONE(ID),
CONSTRAINT FK_OTHER_GROUP FOREIGN
KEY(OTHER_ID) REFERENCES TABLE_TWO(OTHER_ID)
I've read the documentation and the code I've found is this one:
INDEX (product_category, product_id),
INDEX (customer_id),
FOREIGN KEY (product_category, product_id)
REFERENCES product(category, id)
ON UPDATE CASCADE ON DELETE RESTRICT,
FOREIGN KEY (customer_id)
REFERENCES customer(id)
It doesn't quite work for me. Is there any special way to define these indexes? I haven't met them before. The first example had a problem that data types weren't specified. But I'd like someone to explain me how could I do it the second(oracle documentation) way.
This is how I understood the problem:
there are two tables, each having primary key constraint
in my example, those are t_emp and t_dept
there's also the third table whose columns are supposed to reference primary keys from previous two tables
those are fk_th_emp and fk_th_dep foreign key constraints
If that's so, here's how to do that:
SQL> create table t_emp
2 (empno number constraint pk_temp primary key,
3 ename varchar2(20)
4 );
Table created.
SQL> create table t_dept
2 (deptno number constraint pk_dept primary key,
3 dname varchar2(20)
4 );
Table created.
SQL> create table third
2 (id number constraint pk_third primary key,
3 other_id number,
4 --
5 constraint fk_th_emp foreign key (id) references t_emp (empno),
6 constraint fk_th_dep foreign key (other_id) references t_dept (deptno)
7 );
Table created.
SQL>
From what I have been told and read online, I need to create an index for a foreign key even if this exact column already has an index as a primary key. But how to do that? If I simply use this
create index document_fk_i on document(id);
Won't it simply create a second identical index to the first one? (the first one was created automatically by Oracle)
You can't index the same column twice. If there's an index on document.id column because it is a primary key, then you don't (and can't) create another index which would be used for that column's "foreign key constraint" role.
Master table:
SQL> create table test_a (id number primary key);
Table created.
Detail table: ID is a primary key and Oracle will create an index:
SQL> create table test_b (id number primary key);
Table created.
Create a foreign key constraint from detail to master table:
SQL> alter table test_b add constraint fk_ba foreign key (id)
2 references test_a (id);
Table altered.
Try to create additional index on detail's ID column:
SQL> create index idxb on test_b (id);
create index idxb on test_b (id)
*
ERROR at line 1:
ORA-01408: such column list already indexed
SQL>
Hello there i am studying for the Oracle Certification of SQL Associate .
And trying to do some Examples .
I have an issue where i cannot find easily a reference on this .
create table employees
(employee_id number NOT NULL,
first_name varchar(20),
last_name varchar(30),
constraint employee_pk primary key (employee_id));
create table employee_notes
(employee_notes_id number,
employee_notes varchar(500),
constraint pk_employee_notes primary key (employee_notes_id));
create sequence employee_notes_seq start with 1 increment by 1
Now i want to add a new column at employee_notes table with a foreign key constraint .
I can't find out in syntax where is the problem .
****alter table employee_notes
add employee_id number
constraint fk_employee_notes foreign key (employee_id) references employees (employee_id);****
i get this error
ORA-02253: constraint specification not allowed her
I also tried to alter the table and add column and then the constraint but cannot
alter table employee_notes
add employee_id number;
--
alter table employee notes
add constraint fk_employee_notes foreign key (employee_id) references employees (employee_id);
ORA-02253: constraint specification not allowed here
I would like to know how i can do this
and why this syntax is wrong :)
You did something wrong because - it works OK:
SQL> CREATE TABLE employees
2 (
3 employee_id NUMBER NOT NULL,
4 first_name VARCHAR (20),
5 last_name VARCHAR (30),
6 CONSTRAINT employee_pk PRIMARY KEY (employee_id)
7 );
Table created.
SQL>
SQL> CREATE TABLE employee_notes
2 (
3 employee_notes_id NUMBER,
4 employee_notes VARCHAR (500),
5 CONSTRAINT pk_employee_notes PRIMARY KEY (employee_notes_id)
6 );
Table created.
SQL> ALTER TABLE employee_notes ADD employee_id NUMBER;
Table altered.
SQL> ALTER TABLE employee_notes ADD CONSTRAINT fk_employee_notes
2 FOREIGN KEY (employee_id)
3 REFERENCES employees (employee_id);
Table altered.
SQL>
When you use ALTER TABLE ... ADD in order to add a column and a constraint in one statement, do the following:
-- notice the () and the comma!
alter table employee_notes
add (
employee_id number
, constraint fk_employee_notes
foreign key (employee_id) references employees (employee_id)
) ;
That should do the trick. See dbfiddle. The syntax is similar to CREATE TABLE, where you'd also write all column names, data types etc in (), separated by commas.