There is a requirement in our application to create the unique primary key which depend on the value of another unique column (ERROR_CODE). But our application is in a geo active active environment (have several active databases which are synchronized using another program).
Therefore even-though we have a unique constraint on this ERROR_CODE field, there is a possibility that each database has a row with a different PK for the same ERROR_CODE. During the database synchronization, this is a problem, because there are some child tables which has the PK stored in one DB and other rows contain the PK stored in other DB. Because of the unique constraint of ERROR_CODE, sync process cannot move both rows to each database (which is also not a good thing to do).
So there is a suggestion to use the hash of the ERROR_CODE field as the PK value.
I would like to know whether we can define a function based Primary key in oracle?
If PK field is "ID",
"ID" should be equal to ora_has(ERROR_CODE).
Is it possible to define the primary key like that in oracle?
In Oracle 10 you cannot do this, but in Oracle 11 you can. You have to create a virtual column, such columns can be used also as primary key:
ALTER TABLE MY_TABLE ADD (ID NUMBER GENERATED ALWAYS AS (ora_has(ERROR_CODE)) VIRTUAL);
ALTER TABLE MY_TABLE ADD CONSTRAINT t_test_pk PRIMARY KEY (ID) USING INDEX;
Related
I need a column which should store more than 4000 characters(to be exact: between 4000 to 8000). And I want that particular column to be a primary key. Since I have dependency in UI end for that particular column to be primary key.
I tried CLOB and varchar(max) but those datatypes doesn't allow primary key property.
Can anyone help me with a proper datatype which can satisfy both conditions?
I'm using Oracle SQL developer 18.3.0.277
You cannot specify a primary key or unique constraint on a CLOB column. If you try then you get the exception:
ORA-02329: column of datatype LOB cannot be unique or a primary key
You can have a composite primary key with two VARCHAR2(4000) columns:
CREATE TABLE table_name (
value_start VARCHAR2(4000),
value_end VARCHAR2(4000),
CONSTRAINT table_name__value__pk PRIMARY KEY (value_start, value_end)
);
Or, from Oracle 12, you can set the system setting MAX_STRING_SIZE to be extended and can use:
CREATE TABLE table_name (
value_start VARCHAR2(8000) PRIMARY KEY
);
However
I would question the design choice of using a VARCHAR2(8000) column as a primary key as you will need to duplicate the (large) column value in all the referential constraints. Instead, make the value UNIQUE and provide a IDENTITY column which can act as the primary key with a one-to-one correspondence to the large string values.
1.In which order should we apply primary key, foreign key constraints and create index if the Oracle table has millions of data and does not have prior constraints?
2.Can we use 'NOLOGGING PARALLEL' while applying primary key and foreign key constraints like we do while applying(creating) indexes? Or any other method so that primary key and foreign key constraints could be applied faster?
Note: I'll use bullets so that it is easier to read, as it is easy to get lost in long sentences.
My thoughts on the subject; see if anything of this helps.
Well,
as you can't create a foreign key constraint if column(s) it references aren't part of primary or unique key
you'll obviously first have to create primary key constraints
and then foreign key constraints
When you
create a primary key constraint,
Oracle automatically creates index that supports it, unless there's already an index you can use (with the USING INDEX clause)
which means that you can "skip" some indexes (those for primary key constraints as they'll already exist) and virtually save some time
and create "other" indexes
On the other hand,
if you first create unique index on future primary key columns and
later add primary key constraint with the USING INDEX clause, Oracle will "skip" check for possible duplicate values because unique index won't allow them
The same goes for
NOT NULL constraint on future primary key columns; primary key doesn't allow NULLs so - if a column already is NOT NULL, enforcing primary key constraint can skip NULL check as well
I don't know
which columns you'll additionally index, but - as you're on Oracle 11g -
don't forget to index all foreign key constraint columns
because you might encounter unexpected table locks if you
update primary key column in parent table, or
delete parent record
Can you do it with no logging and in parallel? Yes:
SQL> create table test (id number, name varchar2(20));
Table created.
SQL> create unique index ui1_test_id on test (id) nologging parallel 20;
Index created.
SQL> alter table test add constraint pk_test primary key (id) using index ui1_test_id nologging parallel 20;
Table altered.
SQL>
But you'll probably want to change the index and table back to NOPARALLEL and LOGGING when the initial creation is done.
SQL> alter index ui1_test_id noparallel;
Index altered.
SQL> alter table test logging noparallel;
Table altered.
I'm using pl sql developer 12.what i want is to add the make the primary key sequential using oracle 12' windows and forms , not by scripting. I can't find out how?.
aslo, how can i make one to one relation between 2 tables (user,role), in user table i added role_id as foreign key; but the relation seem one to many!!!
In Oracle 12c and above, you define that column as identity columns:
CREATE TABLE mytable (
id NUMBER GENERATED ALWAYS AS IDENTITY,
-- other columns ...
);
A #Mureinik already said, in Oracle 12 and higher versions you can define your primary key column as NUMBER GENERATED ALWAYS AS IDENTITY to get a unique sequential value.
To enforce a one-to-one relationship in the database you'd want to have your ROLE_ID column defined as a primary key on one table, and as either a UNIQUE or PRIMARY key on the second table, with a foreign key relationship between the tables. In other words:
CREATE TABLE T1 (ROLE_ID NUMBER
CONSTRAINT PK_T1
PRIMARY KEY
...);
CREATE TABLE T2 (ID_T2 NUMBER
PRIMARY KEY,
ROLE_ID NUMBER
CONSTRAINT T2_U1
UNIQUE
CONSTRAINT T2_FK1
REFERENCES T1(ROLE_ID)
ON DELETE CASCADE,
...);
After the above ROLE_ID will be the primary key on T1, a unique key on T2, and T2.ROLE_ID will be a foreign key to T1.
Best of luck.
what I have done lastly is that i downloaded sql developer 64 w, and from it; I connected with the database then I made the column sequential
I read that we cannot create a primary key on a column in a Hive table. But I saw the below DDL in some other place and executed it. It worked without any problem.
create table prim(id int, name char(30))
TBLPROPERTIES("PRIMARY KEY"="id");
After this I executed "describe formatted prim" and got to see that a key is created on the column ID
Table Parameters:
PRIMARY KEY id
I inserted two records with same ID number into the table.
insert into prim values(1,'ABCD');
insert into prim values(2,'EFGH');
Both the records were inserted into the table. What baffles me is that we cannot give the PRIMARY KEY in the create statement which I can understand, but when given in TBLPROPERTIES("PRIMARY KEY"="id") how different is it to the primary key in RDBMS.
PRIMARY KEY in TBLPROPERTIES is for metadata reference to preserve column significance. It does not apply any constrain on that column. This can be used as a reference from design perspective.
I have a table with Col1 and Col2 as a composite primary key pk_composit_key and a unique index that was automatically created for the constraint.
I then altered the table to add new column Col3.
I dropped the pk_composit_key constraint:
ALTER TABLE table_name DROP CONSTRAINT pk_composit_key;
Now, When I tried to insert records I got ORA-00001: unique constraint pk_composit_key violated.
Why am I getting that error?
When the key was dropped why wasn't the unique index dropped automatically?
You mentioned exporting and importing the schema, and if that happened in the environment that showed this behaviour it would explain what you're seeing; at least if you used legacy imp rather than the data pump impdp.
The original import documentation states the order objects are imported:
Table objects are imported as they are read from the export dump file. The dump file contains objects in the following order:
Type definitions
Table definitions
Table data
Table indexes
Integrity constraints, views, procedures, and triggers
Bitmap, function-based, and domain indexes
So the unique index would have been imported, then the constraint would have been created.
When you drop a primary key constraint:
If the primary key was created using an existing index, then the index is not dropped.
If the primary key was created using a system-generated index, then the index is dropped.
Because of the import order, the constraint is using an existing index,so the first bullet applies; and the index is retained when the constraint is dropped.
You can use the drop index clause to drop the index even if it wasn't created automatically:
ALTER TABLE table_name DROP CONSTRAINT pk_composit_key DROP INDEX;
See also My Oracle Support note 370633.1; and 1455492.1 suggests similar behaviour will occur with data pump import as well. I'm not aware of any way to check if an index is associated with a constraint at this level; there is no difference in the dba_constraints or dba_indexes views when you create the index manually or automatically. Including drop index will make it consistent though.
It depends on how unique index was created...below are the various ways and behaviour
1) first create unique index (on the column for which primary key to be defined) and then add the primary key constraint. In this situation your DDL to add the primary key will utilize the existing unique index. So when you drop the primary key it will not drop the index but only primary key. ==> this is your situation I guess...
2) While creating the table you define the primary key OR when you add the primary key when there was no existing unique index for the column(s) on which primary key to be defined, so system will create a unique index and use it for primary key. So in this case when you drop the primary key the unique index will also get dropped.