I have Oracle 11.2.0.2.0 and a table with unique constraint created by following script:
create table foo (id varchar(26) not null, name varchar(50) not null);
alter table foo add constraint pk_foo primary key (id);
/**/
alter table foo add constraint un_foo unique (name);
I need to drop the unique constraint, which is easy:
alter table foo drop constraint un_foo;
The trouble is: when the database is backuped in SQL Developer and then restored, then the un_foo unique index is created by explicit command placed at /**/ line:
CREATE UNIQUE INDEX un_foo ON foo (name);
Such an explicitly-created index is not deleted by the alter command above. I realized following command works:
alter table foo drop constraint un_foo drop index;
For primary key, similar command alter table foo drop primary key drop index is in documentation or in Oracle Developer Community discussion. Also, this answer at AskTom uses this syntax too (for keep index). However I don't see any reasoning for such syntax in railroad diagram of alter table command.
Question: is the syntax alter table foo drop constraint un_foo drop index legal? If so, based on what documentation or flow in railroad diagram? If not, why the command doesn't fail?
Thanks!
According to #Chris Saxon's answer to my equivalent question posted to AskTom, the syntax is confirmed as working but not present in documentation.
The decision whether it is doc bug or unintended side effect is still unresolved.
I personally decided to rely on the syntax since, among other things, it is advised also in My Oracle Support.
If absolute safety (read: conforming to the documentation) is required, the only possibility is to use statement alter table foo drop unique (name) drop index;.
I summarized (not so substantial) circumstances around this issue in blogpost (in Czech).
Related
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;
I am trying to drop an index :
DROP INDEX PK_CHARGES
but I get this error
cannot drop index used for enforcement of unique/primary key
Why I am getting this error? I will provide further information if you need any.
How to solve it?
Edit I have no primary key in the table, but I found this weird index that I don't remember I had added:
index name = SYS_C0040476 which have the same columns
You can query the ALL_CONSTRAINTS performance view to see which constraint the index is used by, and which table it applies to, e.g:
select owner, constraint_name, constraint_type,
table_name, index_owner, index_name
from all_constraints
where index_name = 'PK_CHARGES';
I would expect the table name to be 'CHARGES', the constraint name to match the index name, and the constraint type to be 'P'. But since you have a table in mind, perhaps the names aren't following a helpful convention. Maybe an old version of the table was renamed, which would leave the constraints against the new name (e.g. CHARGES_BACKUP or something).
You said you click on the table, then on the view. Perhaps you're not looking at the table that the constraint/index is on; or perhaps you're looking at a view on top of the actual table. You also mention a SYS_ index on the same columns - which can't be on the same table. Do you have multiple similar tables, or access to multiple schemas? You shold run the above query for that index too. As mentions above, you might find an old version (or versions) of the table.
Once you've identified which table the constraint is on, you'll need to decide whether you should actually be keeping it, and if not you can remove it by dropping the constraint with an ALTER TABLE command.
The problem with
But I found this weird index that I dont rember I hadve add
comes because you didn't add it. You had a primary key, then you dropped it, but when you do that Oracle doesn't drop the associated unique index that every primary key has.
So when you drop a primary key you have to drop the unique index of that primary key, that amazingly has the same name as the primary key had.
So for dropping a MY_TABLE_PK you must do:
ALTER TABLE MY_TABLE DROP PRIMARY KEY DROP INDEX;
so you ensure that the index is dropped as well.
"from pl/sql I right click on the table"
The problem with IDEs is that they make us feel very productive, because we can do things with just a click instead of writing some code. This is a problem because when something unusual happens the IDE is no good for investigation and we lack the understanding of the underlying structure of the database which we need to help ourselves.
If you want to learn the Oracle database the worst thing you can do is download SQL Developer or PLSQL Developer or TOAD. They're all fine tools but the only people who should use them are the people who don't need to use them.
the following worked for me with unique index:
ALTER INDEX UX_CHARGES UNUSABLE
/
DROP INDEX UX_CHARGES
/
see: https://docs.oracle.com/cd/E18283_01/server.112/e17120/indexes004.htm#insertedID3
I have a few non-unique constraints that I want to alter into unique constraints ( business rules have changed since the data model was made ). Is there any way to do it with out dropping and recreating as a unique constraint? I was thinking there would be an option in the alter constraint command, but I have not found anything.
Thanks!!
You cannot convert a non-unique index into a unique index.
(It's difficult to say what cannot be done. I'm basing this answer on looking at the ALTER INDEX page of the SQL Language Reference, searching for the word UNIQUE, and not finding any relevant hints. I looked at 11g instead of 10g, but that's probably better in this case because there are a few features that exist in 10g but are only documented in 11g.)
However, you can use a non-unique index for a unique constraint. But there are some performance considerations: a unique index would be smaller and faster.
create table my_table(a number);
create index my_table_index on my_table(a);
alter table my_table add constraint my_table_unique unique (a)
using index my_table_index;
You can't modify a constraint in the way you wish you can only drop and recreate it. If you want to do this with no downtime then look into the DBMS_REDEFINITION package.
In my case, just do drop and re-create the index:
DROP INDEX index_name;
CREATE UNIQUE INDEX index_name ON table_name (col01,col02) TABLESPACE indx;
I'm trying to create a constraint on the OE.PRODUCT_INFORMATION table which is delivered with Oracle 11g R2.
The constraint should make the PRODUCT_NAME unique.
I've tried it with the following statement:
ALTER TABLE PRODUCT_INFORMATION
ADD CONSTRAINT PRINF_NAME_UNIQUE UNIQUE (PRODUCT_NAME);
The problem is, that in the OE.PRODUCT_INFORMATION there are already product names which currently exist more than twice.
Executing the code above throws the following error:
an alter table validating constraint failed because the table has
duplicate key values.
Is there a possibility that a new created constraint won't be used on existing table data?
I've already tried the DISABLED keyword. But when I enable the constraint then I receive the same error message.
You can certainly create a constraint which will validate any newly inserted or updated records, but which will not be validated against old existing data, using the NOVALIDATE keyword, e.g.:
ALTER TABLE PRODUCT_INFORMATION
ADD CONSTRAINT PRINF_NAME_UNIQUE UNIQUE (PRODUCT_NAME)
NOVALIDATE;
If there is no index on the column, this command will create a non-unique index on the column.
If you are looking to enforce some sort of uniqueness for all future entries whilst keeping your current duplicates you cannot use a UNIQUE constraint.
You could use a trigger on the table to check the value to be inserted against the current table values and if it already exists, prevent the insert.
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_triggers.htm
or you could just remove the duplicate values and then enfoce your UNIQUE constraint.
EDIT: After Jonearles and Jeffrey Kemp's comments, I'll add that you can actually enable a unique constraint on a table with duplicate values present using the NOVALIDATE clause but you'd not be able to have a unique index on that constrained column.
See Tom Kyte's explanation here.
However, I would still worry about how obvious the intent was to future people who have to support the database. From a support perspective, it'd be more obvious to either remove the duplicates or use the trigger to make your intent clear.
YMMV
You can use deferrable .
ALTER TABLE PRODUCT_INFORMATION
ADD CONSTRAINT PRINF_NAME_UNIQUE UNIQUE (PRODUCT_NAME)
deferrable initially deferred NOVALIDATE;