Composite primary key on very large tables...

Hello
So I'm building a database where one of the tables will eventually have > 1 billion rows and was wondering about the primary key. The table will have 3 columns (sample_id, object_id, value) and so I was thinking instead of creating a surrogate key I would create a composite primary key on those 3 columns.... People will query either for sample_id = X or object_id = Y. I've created a composite index on object_id, sample_id and value and the query times have been fast < 2-3s per object_id. Although building that index takes some time (7-8 hrs) what would be the pros/cons to composite PK vs a unique index? I plan to do massive bulk uploads (50M records at a time) so I'll disable the constraints before loading.... These records will also be loaded in order so would a clustered table be appropriate?
thanks
steve

Hi,
As correctly said by steve,partition the table.
Create a unique index on single column and then even if ur query is not using that column which has index,use a HINT and make it to use the index.
If ur using joins on this table with other tables u can use use_hash hint which will improve performance.
Hope it helps.
Thanks

Similar Messages

Master Detail Forms with 2 composite primary keys - Is there a workaround?

Hello All,
I have been searching for a workaround to the maximum 2 part primary key restriction on the multi-row updates, and master-detail forms, and am hoping that someone can help me. I am using HTMLDB v2.0.0.00.49 with IE 6 against a 9.2 DB.
I successfully implemented the workaround of Fred Stoopendaal's (see Updata PK on HTML DB ) and it works fine for single page multi-record updateable forms, but alas I haven't been able to extend it to master detail forms (I think it is something to do with Oracle not allowing the "returning" clause on views).
Here is what I tried:
two tables, one with a 2 part composite primary key, which is the master table, and a detail table with 3 part composite primary key -
--------- BEGIN SQL ---------
create table master_table
( master_col1 number
, master_col2 number
, master_col3 varchar2(30)
, constraint master_pk primary key (master_col1,master_col2));
create table detail_table
(detail_col1 number
,detail_col2 number
,detail_col3 number
,detail_col4 varchar2(30)
, constraint detail_pk primary key(detail_col1,detail_col2,detail_col3)
, constraint master_detail_fk foreign key (detail_col1,detail_col2) references master_table(master_col1,master_col2));
create or replace view v_master_table as
select rowid mata_rowid,mata.*
from master_table mata;
create or replace view v_detail_table as
select rowid deta_rowid,
(select rowid from master_table mata where mata.master_col1 = deta.detail_col1 and mata.master_col2 = deta.detail_col2) deta_mata_rowid
, deta.*
from detail_table deta;
create or replace trigger mata_ins_upd_trg
instead of insert or update on v_master_table
referencing new as new old as old
for each row
begin
if inserting then
insert into master_table (master_col1, master_col2, master_col3)
values (:new.master_col1, :new.master_col2, :new.master_col3);
end if;
if updating then
update master_table
set master_col1 = :new.master_col1,
master_col2 = :new.master_col2,
master_col3 = :new.master_col3
where rowid = :old.mata_rowid;
end if;
end;
create or replace trigger deta_ins_upd_trg
instead of insert or update on v_detail_table
referencing new as new old as old
for each row
begin
if inserting then
insert into detail_table ( detail_col1, detail_col2, detail_col3, detail_col4)
values (:new.detail_col1, :new.detail_col2, :new.detail_col3, :new.detail_col4);
end if;
if updating then
update detail_table
set detail_col1 = :new.detail_col1,
detail_col2 = :new.detail_col2,
detail_col3 = :new.detail_col3,
detail_col4 = :new.detail_col4
where rowid = :old.deta_rowid;
end if;
end;
--------- END SQL ---------
Then I created a master-detail form in Apex on the two views, using the mata_rowid and deta_rowid as primary keys, and mata_rowid=deta_mata_rowid as the link. I realise that using a function to fetch the master rowid within the detail view query is costly, but it was my intention to modify the record fetch queries to use the real FK columns once things were up and running.
It seems to generate the pages ok, and I can insert/update master table records, but as soon as I modify records in the detail table things go a bit haywire. I can't find any documentation on how the inbuilt MRU/MRD logic works, so can't figure out the issue.
Can anyone out there tell me what the problem is with the logic above, or if they have come up with a neat solution to this annoying limitation. I know that many will say that I should modify the data model to use surrogate primary keys, but many of the uses for HTMLDB are new interfaces for old schemas, so a workaround that doesn't involve wholesale data model changes would be preferable.
Thanks in advance,
Mike Cretan

Hi, this is likely not the most elegant way...but perhaps the simplest -- and I didn't have much time to play.
I used Wizard to create two separate Master Detail forms, each with a separate detail table. Thus I ended up with four pages:
Page "A" - "Selector" page for Master (Report), with Edit link driving to Detail-1
Page "B" - Editable Master/Detail-1 page (HTML / Report)
Page "C" - "Selector" page for Master (Report), with Edit link driving to Detail-2
Page "D" - Editable Master/Detail-2 page (HTML / Report)
Then I selected the primary key column TWICE on the Report on Page A. Modified the second instance of this column to navigate to Page D (passing primary key) exactly the way the original instance of this column navigates to Page B. Then I deleted Page C.
Since you can have only one Tabular Entry form per page, this seemed the best way to drive two separate detail tables from a common interface.

Reconciling composite primary key tables in 9.0.1.4 DB app connector

Hi
I am trying to get the reconciliation in the 9.0.1.4 db app connector to work on a view that has a composite primary key (one user_id field and one group_id field)
There are no examples on how to do this and my "trial-and-error" efforts have not been fruitful this far. Anyone that has any experience of how to solve this problem?
Best regards
/Martin

Hi Martin, our customer is also very sensitive to changes in his HR system, it is a custom oracle development. He provide us a read only view every day with all changes on their identities. We have developed a custom pl/sql proccess to fill a custom local table with the right information . Then we use this table locally with dbtable connector but with some custom addons.
So i believe that using a second table and keep in synch it is the best approach.
We have detect some problem with 9.0.1.4 DB app connector, it is using internally only one db connection for all its operations, in a huge load condition its can produce errors and race condition problems. We have a custom connector now and it is using connection pool from application server so we will have not this problem.
I believe that oracle should release source for their connectors, i am very sure that partners and customers can improve it.

How to define Composite primary key for a Table

Hi ,
I am basically more into Java Programming , with little bit knowledge on Oracle as DataBase .so please excuse for my silly doubts .
Can anybody please tell me how to define a Composite Primary Key on a Table .
Thanks in advance .
Edited by: user672373773 on Sep 25, 2009 8:54 AM

Here is an example right out of the Oracle documentation and the syntax for adding PK since you mention adding a composite PK.
Example creating composite index
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_indexing.htm#sthref594
Syntax for adding a PK (composite or not)
alter table oooooooo.tttttttt
add constraint tttttttt_PK
primary key (sample_column2,
sample_column1)
using index
tablespace IDXSPC
pctfree 05
initrans 04
maxtrans 08
storage (initial 16k
next 16k
maxextents 32
pctincrease 0);
-- dictionary management with restricted storage, change as desired.
HTH -- Mark D Powell --

Multiple composite primary key in Master Table

Dears ,
I am try to find any solution about Multiple composite primary key by search in forum , but i didn't success ... i am try to built master detail , the master structure table built with multiple composite primary key , i know that apex 4.2 still support tow primary key , in detail table i solved the problem by depend on rowid , and now i can use multiple composite primary key in detail table , the problem with master table because it's support only tow primary key , there are any solution by manual process or any something else ?
Thanks
Abo Yahya

Hi,
I've never done this so all I can do is give some suggestions. It takes more effort because you are going beyond what APEX currently supports. That said, you might try searching the forum with this search string:
key AND table AND instead
Make sure the ANDs are capitailized in the search criteria. Also, look at this thread {thread:id=395870} and the forum thread asociated with this message {message:id=10542916}.
Best wishes,
Howard

Composite primary key in oe_order_headers_all table?

Hi all
What are columns involved in composite primary key in oe_order_headers_all table? how to identify that?
(Order_number, order_type, org_id) are the combination of composite primary key or anything else ?

select * From all_constraints where table_name = 'OE_ORDER_HEADERS_ALL'
SELECT AIC.* FROM ALL_INDEXES AI, ALL_IND_COLUMNS AIC
WHERE AI.TABLE_NAME='OE_ORDER_HEADERS_ALL'
AND AI.UNIQUENESS='UNIQUE'
AND AI.INDEX_NAME = AIC.INDEX_NAME
order by AI.INDEX_NAME
Hope this helps,
Sandeep Gandhi

Update enrolled table which has 6 composite primary key

Hi Everyone,
I am trying to update a grade column in table called enrolled which has 6 composite primary key column including SID, TERMYEAR, FACCODE, DEPCODE, COURSENO, SECNO and 2 extra column including GRADE, IDD all of them are of type VARCHAR2 as describe below:
To update this table I used the command below:
UPDATE enrolled
SET grade = :COURSE_BLOCK.GRADE_TEXT
WHERE IID = :GLOBAL.logUserid
AND SID = :COURSE_BLOCK.SID_TEXT
AND FACCODE = :COURSE_BLOCK.FACULTY_TEXT
AND DEPCODE = :COURSE_BLOCK.DEPARTMENT_TEXT
AND COURSENO = :COURSE_BLOCK.COURSE_TEXT
AND SECNO = :COURSE_BLOCK.SECTION_TEXT;
Note: the :GLOBAL.logUserid is a global variable that I assigned the user id when the user log on to the application.
When I run the application and fill out the form in order to update the table this doesn't update the table and if I use SQL*PLUS as well with the values that I use for the form to update the table I get message: o rows updated
Can Someone help please?

Here is the solution.
The problem:
The problem was that the enrolled table was designed in a way that a student can enrolled in the lecture(LEC type column) and Laboratory(LAB type column). When a student is given a grade, it is given a grade for the course 100 (eg: 03-60-100) this course has a lecture and lab. this course belong to the faculty code 03(science) department 60 (computer Science) so when a student register to a course, will register to a lecture and a lab but he will receive a grade for the course 100 lec in this case Oracle couldn't update the table because there was two column with course 100 for that particular student Id
The solution:
There are many solution I believe but my quickest solution is when a student register to the course by default is given a grade 'I' means Incomplete then when the instructor add the grade, he can just update a grade from incomplete to the final grade (eg A) now the code will be to get only the course 100 that has grade and discard that doesn't have grade this means that I need only to make sure that the WHERE Clause grade is not null shown below.
UPDATE enrolled
SET grade = BLOCK_NAME.FIELD_NAME
WHERE grade IS NOY NULL
AND IID = BLOCK_NAME.FIELD
AND faccode = BLOCK_NAME.FIELD
AND depcode = BLOCK_NAME.FIELD
AND courseno= BLOCK_NAME.FIELD_NAME
NAD secno = BLOCK_NAME.FIELD_NAME
AND SID = BLOCK_NAME.FIELD_NAME

How to Alter any table to make some fields Composite Primary Key

I need to Alter Table to make some fields Composite Primary Key.
Is it possible to do this ?
Please give any example.
Regards,
AgrawalV

Agrawal
If you are looking for an example to create a composite primary key, here you are.
sql> Alter Table myTable add constraint pk_myTable primary key(col1, col2, ...coln) ;
where
pk_myTable is the name of the primary key constraint,
myTable is the name of the table that you want to create a constraint on and
col1...coln are the column names in the table <myTable)

Composite Primary key & Primary key questions

Background:
1.5 TB data warehouse. All tables use at least a 3 column composite Primary key. Most use 3. col1||col2||col3 to achieve uniqueness.
col1= very low cardinality. 99% of the values are '0'
col2 = high cardinality. (SSN's, loaded monthly)
col3 = low cardinality. (monthly sequence number used for partitioning)
From what I've read, the first column used in a composite primary key also receives its own index. If that is correct, then the primary key being used is losing its effectiveness by putting a very low cardinality column as the first column of the Primary key. By moving col2 to the first position of the composite key, I would be obtaining an index on SSN which would be much more useful. (Please correct me if I'm wrong) Or since the index would be so large anyway, the CBO would just do full table scans which is what I'm trying to get away from.
This Primary key is used to ensure uniqueness during loads. Other than that, it really has no purpose and is never queried by the user. (WHERE col1||col2||col3 = xxxxxxxxx)
As a DBA, I see this massive tablespace for holding the primary keys now reaching in excess of 157 GB and it seems like such a waste of space. The problem I'm running across is how to ensure uniqueness during the loads w/o having to store the unique values. (the 157 GB) If I drop the PK's, then create unique indexes just for the loads, then the unique index would be generated against the entire table, which would take forever.
If you create a local index (what I want in the end) it still has to create the index for all previous partitions (250+ partitions). You can't create a specific 'local' index on a partition. You create a local index on the table and when a new partition is added, the index is then added as well. That's what I want to do with some of my fields like SSN but for loading purposes, this isn't going to help me.
I need a way to ensure uniqueness during a monthly load of a new partition (col1||col2||col3) but w/o having to store these values for eternity. Right now it's the primary key, so it has to be stored. I hope I'm making sense here. Any ideas?

I think you need some clarification about the index supporting the primary key.
The primary key is unique - the database will enforce this for you.
All of the columns in the primary key are in the index that enforces the key (not just the first column).
Usually this index is a unique index, but you can have a non-unique index supporting a primary key.
I'm a little confused with some of your other statements
how to ensure uniqueness during the loads w/o having to store the unique valuesIf you don't store the value how do you know it is unique?
Did you mean that you don't want to store the key values in both the table and the index?
You may want to consider making col3 (the partition key) the leading column of the index, so you can create a local (instead of global) PK index.
I wouldn't worry too much about col1 (the column full of mostly zeros) - numbers are stored variable length. A NUMBER(38) that holds a zero takes no more space than a NUMBER(1) that holds a zero.

Creation of CMP bean for a Composite Primary key????

Hi
i am having a composite primary keys in one of my table in the database.
I am trying to create a new entity bean for this table but i don't know how to create one in case when there is a composite primary key for a table.
Can anybody let me know is it possible to do it.
what is the procedure to be followed for the creation of the Entity bean in case of a composite primary key.
I am using MySql as the database .Creating CMP type of Entity bean.
Any help in this regard will be greatly useful to me as this is very urgent.
Thanks & Regards
Vikram K

Hi Nikola,
There are several problems with your CMP bean.
1. Fields of a Primary Key Class must be a subset of CMP fields, so yes, they must be either a primitive or a Serializable type.
2. Sun Application Server does not support Primary Key fields of an arbitrary Serializable type (i.e. those that will be stored
as BLOB in the database), but only primitives, Java wrappers, String, and Date/Time types.
Do you try to use stubs instead of relationships or for some other reason?
If it's the former - look at the CMR fields.
If it's the latter, I suggest to store these fields as regular CMP fields and use some other value as the PK. If you prefer that
the CMP container generates the PK values, use the Unknown
PrimaryKey feature.
Regards,
-marina

How to Work with Composite Primary Key

Hi All,
I'm working with Toplink JPA. Here I have A problem with inserting into database table which have composite Primary Key.
What I'm doing is, I have two tables. to maintain many to many relation between these two tables I created another intermediate table which consists of foreign Keys (reference) of above two tables.
Now these two foreign Keys in the Intermediate table made as composite Primary Keys.
When I'm trying to the data in the Intermediate table I'm getting the foreign Keys values are null..
could anyone suggest me how to work with composite Primary Keys
Thanks,
Satish

I have the same problem, I have 3 tables with a join table joining them all. I have created an intermediate table entity. When I go to create a an entry, it says that I cannot enter null into "ID". Here is the SQl toplink generates:
INSERT INTO Z_AUTH_USER_AUTHORIZATION (CONTEXT_ID, AUTHORIZATION_ID, USER_ID) VALUES (?, ?, ?)
bind => [null, null, null]
Here are the classes:
-----------------------Join Table-----------------------------------------------
@Entity()
@Table(name = "Z_AUTH_USER_AUTHORIZATION")
public class AuthUserAuthorization implements Serializable{
@EmbeddedId
private AuthUserAuthorizationPK compId;
// bi-directional many-to-one association to AuthAuthorization
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "AUTHORIZATION_ID", referencedColumnName = "ID", nullable = false, insertable = false, updatable = false)
private AuthAuthorization authAuthorization;
// bi-directional many-to-one association to AuthContext
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "CONTEXT_ID", referencedColumnName = "ID", nullable = false, insertable = false, updatable = false)
private AuthContext authContext;
// bi-directional many-to-one association to AuthUser
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "USER_ID", referencedColumnName = "ID", nullable = false, insertable = false, updatable = false)
private AuthUser authUser;
---------------------------------------User table--------------------------------------------------------------
@Entity()
@Table(name = "Z_AUTH_USER")
public class AuthUser implements Serializable, IUser{
@Id()
@SequenceGenerator(name = "AUTH_USER_ID_SEQ", sequenceName = "Z_AUTH_USER_ID_SEQ")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "AUTH_USER_ID_SEQ")
@Column(name = "ID", unique = true, nullable = false, precision = 10)
private Integer id;
// bi-directional many-to-one association to AuthUserAuthorization
@OneToMany(mappedBy = "authUser", fetch = FetchType.EAGER)
private java.util.Set<AuthUserAuthorization> authUserAuthorizations;
-----------------------------------Context table-----------------------------------------------------------------
@Entity()
@Table(name = "Z_AUTH_CONTEXT")
public class AuthContext implements Serializable, IContext{
@Id()
@SequenceGenerator(name = "AUTH_CONTEXT_ID_SEQ", sequenceName = "Z_AUTH_CONTEXT_ID_SEQ")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "AUTH_CONTEXT_ID_SEQ")
@Column(name = "ID", unique = true, nullable = false, precision = 8)
private Integer id;
// bi-directional many-to-one association to AuthUserAuthorization
@OneToMany(mappedBy = "authContext", fetch = FetchType.EAGER)
private java.util.Set<AuthUserAuthorization> authUserAuthorizations;
----------------------------Authorization table-------------------------------------------------
@Entity()
@Table(name = "Z_AUTH_AUTHORIZATION")
public class AuthAuthorization implements Serializable, IAuthorization{
@Id()
@SequenceGenerator(name = "AUTH_AUTHORIZATION_ID_SEQ", sequenceName = "Z_AUTH_AUTHORIZATION_ID_SEQ")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "AUTH_AUTHORIZATION_ID_SEQ")
@Column(name = "ID", unique = true, nullable = false, precision = 8)
private Integer id;
// bi-directional many-to-one association to AuthUserAuthorization
@OneToMany(mappedBy = "authAuthorization", fetch = FetchType.EAGER)
private java.util.Set<AuthUserAuthorization> authUserAuthorizations;
I have tried to create the new entity several ways. I have tried to create one with the default constructor then set this entity on each of the other entities, I have also tried to pass in the entities to the join entity and set them there, but this doesn't work. Any help would be very appreciated!
Thanks,
Bill

Error While Deploying A CMP Entity Bean With A Composite Primary Key

Hello all,
I have a problem deploying CMP Entity beans with composite primary keys. I have a CMP Entity Bean, which contains a composite primary key composed of two local stubs. If you know more about this please respond to my post on the EJB forum (subject: CMP Bean Local Stub as a Field of a Primary Key Class).
In the mean time, can you please tell me what following error message means and how to resolve it? From what I understand it might be a problem with Sun ONE AS 7, but I would like to make sure it's not me doing something wrong.
[05/Jan/2005:12:49:03] WARNING ( 1896):      Validation error in bean CustomerSubscription: The type of non-static field customer of the key class
test.subscription.CustomerSubscriptionCMP_1530383317_JDOState$Oid must be primitive or must implement java.io.Serializable.
     Update the type of the key class field.
     Warning: All primary key columns in primary table CustomerSubscription of the bean corresponding to the generated class test.subscription.CustomerSubscriptionCMP_1530383317_JDOState must be mapped to key fields.
     Map the following primary key columns to key fields: CustomerSubscription.CustomerEmail,CustomerSubscription.SubscriptionType. If you already have fields mapped to these columns, verify that they are key fields.Is it enough that a primary key class be serializable or all fields have to implement Serializable or be a primitive?
Please let me know if you need more information to answer my question.
Thanks.
Nikola

Hi Nikola,
There are several problems with your CMP bean.
1. Fields of a Primary Key Class must be a subset of CMP fields, so yes, they must be either a primitive or a Serializable type.
2. Sun Application Server does not support Primary Key fields of an arbitrary Serializable type (i.e. those that will be stored
as BLOB in the database), but only primitives, Java wrappers, String, and Date/Time types.
Do you try to use stubs instead of relationships or for some other reason?
If it's the former - look at the CMR fields.
If it's the latter, I suggest to store these fields as regular CMP fields and use some other value as the PK. If you prefer that
the CMP container generates the PK values, use the Unknown
PrimaryKey feature.
Regards,
-marina

HOW TO GET COUNT IN OF COMPOSITE PRIMARY KEYS USING ECLIPSELINK

Hi all,
We are currently migrating our application form oracle 10g to 11 g and hence migrating from toplink to eclipselink.
we are unable to fire the count query and getting the following exception ...
Error Code: 909
Call: SELECT COUNT() FROM T_USER_MESSAGE t0, T_USER t2, T_MESSAGE_RECIPIENT t1 WHERE ((((t2.PERSISTENT_ID = ?) AND (t2.SITE_CODE = ?)) AND (t1.DELETED_BY_RECIPIENT = ?)) AND (((t2.PERSISTENT_ID = t1.RECIPIENT_ID) AND (t2.SITE_CODE = t1.RECIPIENT_SITE)) AND ((t0.PERSISTENT_ID = t1.MESSAGE_ID) AND (t0.SITE_CODE = t1.MESSAGE_SITE))))
bind => [13398610, 1, F]
please advise .
we suspect that this could be because of the composite primary key in one of the tables .
any pointers to specify how count(*) could be used in this scenario would be of great help ..
Thanks in advance

What is the query being used, include the JPQL/expression code.
What is the error message (I assume this is a database error?).
What version are you using, can you try the latest EclipseLink 2.1 release.
James : http://www.eclipselink.org

Null in Composite Primary Key and "Primary keys must not contain null"

Hello all.
I'm a newbie concerning to JPA/EJB3, but I was wondering if toplinks doesn't support composite primary keys with null in some field (something perfectly right in any RDBMS).
I used JDeveloper (I'm using Oracle 10g database and JDeveloper 10.1.3.2.) wizards to generate JPA classes and I checked out generated files (with annotations), so they should be right (by the way, other O-R mappings for my model are working right, but this one).
I'm getting the next error:
Exception Description: The primary key read from the row [DatabaseRecord(
     TSUBGRUPOSLDI.CD_GRUP => 01
     TSUBGRUPOSLDI.CD_SUBGRUP => null
     TSUBGRUPOSLDI.CG_POBL => 058
     TSUBGRUPOSLDI.CG_PROV => 28
     TSUBGRUPOSLDI.DSCR => Sanidad)] during the execution of the query was detected to be null. Primary keys must not contain null.
Compound primary key is (CD_GRUP, CD_SUBGRUP). No foreign keys, no joins (only a NamedQuery: "select o from ..."). It's the simplest case!
I checked out that everything runs ok if there's no "null" value in CD_SUBGRUP.
After some research (this and other forums) I'm beginning to believe that it's not supported, but not sure.
Am I doing sth wrong? If not, what is the reason to not support this? Will it be supported in the future?
Thanks in advance.

Null is a special value and in many databases is not comparable to another null value (hence the isNull operator) and may pose problems when used to uniquely identify an Entity. TopLink does not support null values within a composite PK. As the nullable column is most likely not designated as a PK within your database table (many databases do not allow this) I recommend updating the Entity PKs to match that of the database.
--Gordon

In which case composite primary key allows NULL values in it

Hi to all
In what case composite primary key allows nulls in it.
Let us suppose, I created a composite primary key with 2 attributes.
CREATE TABLE sample
BNK_Id NUMBER(6),
BNK_Name VARCHAR2(20),
CONSTRAINT BNK_Id_Name_PK PRIMARY KEY(BNK_Id,BNK_Name)
When it allows null values in it.
thanks in advance

Are you sure that your instructor was not talking about unique keys? As Solomon said, a primary key always implies not null on all of the columns of the PK. However a unique key does not automatically imply not null, and can have nulls in a column as long as the values in the populated columns are unique.
SQL> create table test (
2     id number,
3     pid number,
4     descr varchar2(10));
Table created.
SQL> alter table test add constraint test_unq
2     unique (id, pid);
Table altered.
SQL> insert into test values (1, null, 'desc1');
1 row created.
SQL> insert into test values (2, null, 'desc2');
1 row created.
SQL> insert into test values (2, null, 'fail1');
insert into test values (2, null, 'fail1')
ERROR at line 1:
ORA-00001: unique constraint (OPS$ORACLE.TEST_UNQ) violatedJohn

Composite primary key on very large tables...

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