So I failed in exam with score 60% which needed 3% for pass, and I want to know about sequence in create table statement, in question given us that =>
in the database "exist" sequence for example SEQ_001 and used in for example=>
SQL>create table ( id number default seq_001.nextval ); or
create table ( id number default seq_001.currval );
And in the topic of 1z0 071 written that =>
This exam was validated against 11g Release 2 version 11.2.0.1.0 and up to 19c
And I know that sequence is possible in create table from 12c but not in previous versions, so how I can know that which version is for this questions and how to check that the exist sequence is used with nextval, exists not means that it is used( I am about nextval after creating, if no currval can give error ). In this type questions I confused.
The following statement
create table t23 ( id number default seq_001.nextval );
succeeds on Oracle 18c (demo on db<>fiddle).
but fails on Oracle 11gR2 with this error:
ORA-00984: column not allowed here
db<>fiddle uses XE editions, but I don't think that's the explanation. So it seems the exam was not "was validated against 11g Release 2 version 11.2.0.1.0" with full rigour.
Regarding the question of Oracle versions for taking the 1z0-071 exam I would say that although there are differences between 11g up to 19c, most of the questions should be based on concepts that are standard between these versions.
More specifically for the Sequence part of the question, although it is possible to create a table with a default value pointing to currval, it would seldom be useful. Using the example of ID above, imagine using this sequence to create user IDs. We would expect different users to have different IDs, and with currval there is a strong possibility that different users would have the same ID making the column essentially useless.
Although not specified in your question, I would assume that most examples of using a sequence default would be for a surrogate primary key, which would need to be unique. Nextval would ensure that these would be unique assuming that rows are not entered with values greater than the existing sequence currval by an outside user.
Related
I am trying to implement my SQLDeveloper DB into Oracle APEX. I cannot figure out how to get the PK's in my table to auto-increment starting from a certain value (i.e. 400001). I have tried making triggers and sequences but when I try to add a row using a form in APEX, my PK increments from 40 for some reason.
Here is my APEX form outcome
enter image description here
Here is how it inserts into SQL Developer
enter image description here
Basically, can someone describe to me how I can edit the existing trigger, or create a sequence, that would make application_id of a new entry auto-increment by 1.
Thanks!
Find max application_id:
select max(application_id) From your_Table;
Suppose it is 400010 (as screenshot suggests). Now recreate the sequence (presuming its name is seq_app):
drop sequence seq_app;
create sequence seq_app start with 400011 increment by 1 nocache;
Trigger is most probably OK, as you see values being inserted into the table.
Side note: sequences will be unique, but not necessarily gapless. CACHE (or NOCACHE) might affect that, but - for performance sake, you'd rather let Oracle cache sequence numbers (default is 20) which means that - if you don't use some of those cached numbers, they will be lost. I wouldn't worry, if I were you.
In my application I have created a column with sequence to have unique id for each and every record that I add,I doubt will there be any unique row-number created by oracle itself for every record we updated in table,if yes then how to access that row number like
SELECT row-number from table where employee_name='name';
here I want to get unique row number created by oracle,
I have searched on net but haven't got proper information
Oracle does maintain a ROWID for each row; however, in my opinion using ROWID in user-written code is both poor practice and dangerous. ROWID is only guaranteed to be constant for the duration of a single transaction. ROWID is not guaranteed to be constant forever and the database can change it if and when it determines that a change is necessary. If your data does not supply a value or combination of values which are unique and unchanging I strongly suggest you learn how to create an artificial key which is automatically set using sequences and triggers. I believe 12c supplies auto-increment columns which you can use if you're using the latest version of Oracle.
Share and enjoy.
There are 2 unique identifiers in Oracle named as ROWNUM and ROWID. You can use them in such ways:-
SELECT ROWNUM
FROM table
WHERE employee_name = 'name';
and
SELECT ROWID
FROM table
WHERE employee_name = 'name';
You can read further about them.
Rownum -
http://docs.oracle.com/cd/B12037_01/server.101/b10759/pseudocolumns008.htm
Rowid - http://docs.oracle.com/cd/B19306_01/server.102/b14200/pseudocolumns008.htm
I'm trying to generate a sorted GUID as a primary key in Oracle. In SQL Server I could use one of the following to sort the rows physically
By clustered primary key as a unique identifier.
By NEWSEQUENTIALID.
I have searched for an Oracle equivalent but failed to find a solution. I know about Is there a way to create an auto-incrementing Guid Primary Key in an Oracle database?, but there's no indication whether SYS_GUID() is sorted.
How could I create a sequential primary key in Oracle?
If you want to create a GUID then SYS_GUID() is what you should be using, you can create this in a table as per the linked question. It's unclear from the documentation whether SYS_GUID() is incrementing. It might be but that's not really a statement that imparts trust.
The next part of your question (and some comments) keeps asking about clustered primary keys. This concept does not exist in the same way in Oracle as it does in SQL Server and Sybase. Oracle does have indexed organized tables (IOT) ...
... a table stored in a variation of a B-tree index structure... rows
are stored in an index defined on the primary key for the table. Each
index entry in the B-tree also stores the non-key column values. Thus,
the index is the data, and the data is the index.
There are plenty of uses for IOTs but it's worth bearing in mind you're altering the physical structure of the database on the disk for "performance reasons". You're doing the ultimate of all premature optimizations using something that has both negative and positive aspects. Read the documentation and be sure that this is what you want to do.
I would generally use an IOT only when you don't care about DML performance but when you do a lot of range scans, or you need to order by the primary key. You create an IOT in the same way as you would an ordinary table, but because everything you want is now part of the table everything goes in your table definition:
create table test_table (
id raw(32) default sys_guid()
, a_col varchar2(50)
, constraint pk_my_iot primary key (id)
) organization index;
It's worth noting that even with an IOT you must use an explicit ORDER BY in order to guarantee returned order. However, because of the way this is stored Oracle can table a few short cuts:
select *
from ( select *
from test_table
order by id )
where rownum < 2
SQL Fiddle.
As with everything, test, don't assume that this is the structure you want.
Oracle has as SYS_GUID() function, which generates a 16-byte RAW datatype. But, I'm not sure what you mean by "sorted GUID". Can you elaborate?
Do you mean you need each generated GUID to sort "after" the previously generated GUID? I looked at the SYS_GUID() function, and it seems to generate GUIDs in sorted order, but looking at the documentation, I don't see anything that says that is guaranteed.
If I understand your question correctly, I'm not sure it's possible.
You may be able to use SYS_GUID() and prepend a sequence, to get your desired sort order?
Can you explain more about your use case?
Adding the following in response to comment:
Ok, now I think I understand. What I think you want, is something called an IOT, or Index Organized Table, in Oracle. It's a table that has an index strucure, and all data is clustered, or grouped by the primary key. More information is available here:
http://docs.oracle.com/cd/E16655_01/server.121/e17633/indexiot.htm#CNCPT721
I think that should do what you want.
When adding a column to a table that has a default value and a constraint of not null. Is it better to run as a single statement or to break it into steps while the database is under load.
ALTER TABLE user ADD country VARCHAR2(4) DEFAULT 'GB' NOT NULL
VERSUS
ALTER TABLE user ADD country VARCHAR2(2)
UPDATE user SET country = 'GB'
COMMIT
ALTER TABLE user MODIFY country DEFAULT 'GB' NOT NULL
Performance depends on the Oracle version you use. Locks are generated anyway.
If version <= Oracle 11.1 then #1 does the same as #2. It is slow anyway.
Beginning with Oracle 11.2, Oracle introduced a great optimization for the first statement (one command doing it all). You don't need to change the command - Oracle just behaves differently. It stores the default value only in data dictionary instead of updating each physical row.
But I also have to say, that I encountered some bugs in the past related to this feature (in Oracle 11.2.0.1)
failure of traditional import if export was done with direct=Y
merge statement can throw an ORA-600 [13013] (internal oracle error)
a performance problem in queries using such tables
I think this issues are fixed in current version 11.2.0.3, so I can recommend to use this feature.
Some time ago we have evaluated possible solutions of the same problem. On our project we had to remove all indexes on table, perform altering and restore indexes back.
If your system needs to be using the table then DBMS_Redefinition is really your only choice.
edit: Look to the end of this question for what caused the error and how I found out.
I have a very strange exception thrown on me from Hibernate when I run an app that does batch inserts of data into an oracle database. The error comes from the Oracle database, ORA-00001, which
" means that an attempt has been made to
insert a record with a duplicate
(unique) key. This error will also be
generated if an existing record is
updated to generate a duplicate
(unique) key."
The error is weird because I have created the same table (exactly same definition) on another machine where I do NOT get the same error if I use that through my app. AND all the data get inserted into the database, so nothing is really rejected.
There has to be something different between the two setups, but the only thing I can see that is different is the banner output that I get when issuing
select * from v$version where banner like 'Oracle%';
The database that gives me trouble:
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Prod
The one that works:
Oracle Database 10g Release 10.2.0.3.0 - 64bit Production
Table definitions, input, and the app I wrote is the same for both. The table involved is basically a four column table with a composite id (serviceid, date, value1, value2) - nothing fancy.
Any ideas on what can be wrong? I have started out clean several times, dropping both tables to start on equal grounds, but I still get the error from the database.
Some more of the output:
Caused by: java.sql.BatchUpdateException: ORA-00001: unique constraint (STATISTICS.PRIMARY_KEY_CONSTRAINT) violated
at oracle.jdbc.driver.DatabaseError.throwBatchUpdateException(DatabaseError.java:367)
at oracle.jdbc.driver.OraclePreparedStatement.executeBatch(OraclePreparedStatement.java:8728)
at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
How I found out what caused the problem
Thanks to APC and ik_zelf I was able to pinpoint the root cause of this error. It turns out the Quartz scheduler was wrongly configured for the production database (where the error turned up).
For the job running against the non-failing oracle server I had <cronTriggerExpression>0/5 * * * * ?</cronTriggerExpression> which ran the batch job every five seconds. I figured that once a minute was sufficent for the other oracle server, and set the quartz scheduler up with * */1 * * * ?. This turns out to be wrong, and instead of running every minute, this ran every second!
Each job took approximately 1.5-2 seconds, and thus two or more jobs were running concurrently, thus causing simultaneous inserts on the server. So instead of inserting 529 elements, I was getting anywhere from 1000 to 2000 inserts. Changing the crontrigger expression to the same as the other one, running every five seconds, fixed the problem.
To find out what was wrong I had to set true in hibernate.cfg.xml and disable the primary key constraint on the table.
-- To catch exceptions
-- to find the offending rows run the following query
-- SELECT * FROM uptime_statistics, EXCEPTIONS WHERE MY_TABLE.rowid = EXCEPTIONS.row_id;
create table exceptions(row_id rowid,
owner varchar2(30),
table_name varchar2(30),
constraint varchar2(30));
-- This table was set up
CREATE TABLE MY_TABLE
(
LOGDATE DATE NOT NULL,
SERVICEID VARCHAR2(255 CHAR) NOT NULL,
PROP_A NUMBER(10,0),
PROP_B NUMBER(10,0),
CONSTRAINT PK_CONSTRAINT PRIMARY KEY (LOGDATE, SERVICEID)
);
-- Removed the constraint to see what was inserted twice or more
alter table my_table
disable constraint PK_CONSTRAINT;
-- Enable this later on to find rows that offend the constraints
alter table my_table
enable constraint PK_CONSTRAINT
exceptions into exceptions;
You have a unique compound constraint. ORA-00001 means that you have two or more rows which have duplicate values in ServiceID, Date, Value1 and/or Value2. You say the input is the same for both databases. So either:
you are imagining that your program is hurling ORA-00001
you are mistaken that the input is the same in both runs.
The more likely explanation is the second one: one or more of your key columns is populated by an external source or default value (e.g. code table for ServiceId or SYSDATE for the date column). In your failing database this automatic population is failing to provide a unique value. There can be any number of reasons why this might be so, depending on what mechanism(s) you're using. Remember that in a unique compound key NULL entries count. That is, you can have any number of records (NULL,NULL.NULL,NULL) but only one for (42,NULL,NULL,NULL).
It is hard for us to guess what the actual problem might be, and almost as hard for you (although you do have the advantage of being the code's author, which ought to grant you some insight). What you need is some trace statements. My preferred solution would be to use Bulk DML Exception Handling but then I am a PL/SQL fan. Hibernate allows you to hook in some logging to your programs: I suggest you switch it on. Code is a heck of a lot easier to debug when it has decent instrumentation.
As a last resort, disable the constraint before running the batch insert. Afterwards re-enable it like this:
alter table t42
enable constraint t42_uk
exceptions into my_exceptions
/
This will fail if you have duplicate rows but crucially the MY_EXCEPTIONS table will list all the rows which clash. That at least will give you some clue as to the source of the duplication. If you don't already have an exceptions table you will have to run a script: $ORACLE_HOME/rdbms/admin/utlexcptn.sql ( you may need a DBA to gain access to this directory).
tl;dr
insight requires information: instrument your code.
The one that has problems is a EE and the other looks like a SE database. I expect that the first is on quicker hardware. If that is the case, and your date column is filled using SYSDATE, it could very well be that the time resolution is not enough; that you get duplicate date values. If the other columns of your data are also not unique, you get ORA-00001.
It's a long shot but at first sight I would look into this direction.
Can you use an exception table to identify the data? See Reporting Constraint Exceptions
My guess would be the service id. Whatever service_id hibernate is using for the 'fresh' insert has already been used.
Possibly the table is empty in one database but populated in another
I'm betting though that the service_id is sequence generated and the sequence number is out of sync with the data content. So you have the same 1000 rows in the table but doing
SELECT service_id_seq.nextval FROM DUAL
in one database gives a lower number than the other. I see this a lot where the sequence has been created (eg out of source control) and data has been imported into the table from another database.