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.
Related
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 want to create a table bar with a named foreign key constraint backed by a named index. I would like to do that with an inline definition in the create table DDL statement. When looking at the Oracle 19 SQL Language Reference it looks like Oracle should support doing this inline.
When executing the following statements...
create table foo (
id number not null primary key
);
create table bar (
id number not null primary key,
nick varchar2(16) not null constraint foo_nick_ck unique using index,
foo_id number not null constraint foo_fk references foo using index
);
Oracle will respond with [42000][907] ORA-00907: missing right parenthesis and point at the position just before the using index on the last line. If I remove using index it works (but without index being created of course). I've kept the column nick as an example of where it works to create the backing index inline, but for a unique constraint instead of a foreign key constraint.
I am aware that a workaround is to create the backing index in a separate DDL statement, but I would very much like to have it neat and tidy inline.
I am aware that a workaround is to create the backing index in a separate DDL statement, but I would very much like to have it neat and tidy inline.
Unfortunately the syntax does not exist to create indexes inline.
The USING INDEX clause is syntactic sugar: Oracle creates indexes to enforce Primary Key and Unique constraints regardless of whether we include that clause (*). This is because an index is necessary to Oracle's implementation of unique constraints. But there is no such need for an index to enforce a foreign key, it's just desirable.
(*) Unless there's an existing index on the constrained column(s) which Oracle can use.
As per Oracle documentation:
You can specify the using_index_clause only when enabling unique or
primary key constraints
You cannot specify this clause for a NOT NULL, foreign key, or
check constraint.
I need to modify an existing PK. Therefore I drop an recreate it.
ALTER TABLE B DROP CONSTRAINT PK_B;
ALTER TABLE B ADD CONSTRAINT PK_B PRIMARY KEY ("TYP", "NR", "HH", "QUART");
Unfortunately the last Statement will give me an error ORA-00955
If I create the PK constraint like it was defined originally with:
ALTER TABLE B ADD CONSTRAINT PK_B PRIMARY KEY ("TYP", "NR", "HH");
everything works fine.
Perhaps there is an INDEX associated with the PRIMARY KEY CONSTRAINT, and it is also named as PK_B.
You can check it as :
SELECT * FROM USER_INDEXES WHERE TABLE_NAME='<table_name>';
If that's true, then do :
ALTER INDEX "PK_B" RENAME TO "PK_XYZ";
Update : Regarding ALTER INDEX statement, few important points as mentioned by Justin in the comments
Oracle implicitly creates an UNIQUE index to support the PRIMARY KEY CONSTRAINT. Since, the index is of the same name that of the primary key, and now that the primary key is being modified, it is better to drop and re-create the index again as per the definition of the old primary key.
My conclusion :
The primary key constraint is enforced through a unique index.
If Oracle already finds an index – unique or non-unique – it uses it
for the primary key.
If the index was initially created as non-unique, it will continue to
show as non-unique, however it will actually be a unique index.
A good demonstration and quite detailed on other aspects too, by Arup : Primary Keys Guarantee Uniqueness? Think Again.
I had the same issue where I had to do the following to delete reference to a table from the view whilst recreating the database from the scratch. I was searching for the same in tables and indexes first.
connect sys/oracle as sysdba;
select * from all_tables
select * from all_indexes
(finally located the reference in the views)
select * from all_views where view_name like '%WKSTSTATE%';
drop view RUEGEN.WKSTSTATE;
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;
I've recently stopped to think that Primary Keys are not indexes, they're a combination of Unique and Null constraints. And till now, I've never created index for PK columns. My question is if I should create index for PK columns if this column is going to be used in the WHERE part of many queries.
Oracle will create an index for you, or can use an existing one. Whether a unique or non-unique index is used is up to you.
http://docs.oracle.com/cd/B28359_01/server.111/b28310/indexes003.htm#i1006566
A primary key itself is not an index, and nor is a unique constraint -- they are both constraints. However an index is used to support them.
A unique index is rather different as it can exist in the absence of a unique or primary key constraint, and neither constraint type require that the index supporting it be unique.