I have this table in an Oracle DB which has a primary key defined on 3 of the data columns. I want to drop the primary key constraint to allow rows with duplicate data for those columns, and create a new column, 'id', to contain an auto-incrementing integer ID for these rows. I know how to create a sequence and trigger to add an auto-incrementing ID for new rows added to the table, but is it possible to write a PL/SQL statement to add unique IDs to all the rows that are already in the table?
Once you have created the sequence:
update mytable
set id = mysequence.nextval;
If you're just using an integer for a sequence you could update the id with the rownum. e.g.
update
table
set id = rownum
You then need to reset the sequence to the next valid id.
Is this what you need?
UPDATE your_table
SET id = your_seq.nextval;
This assumes you don't care what order your primary keys are in.
First you should check your PCTFREE... is there enough room for every row to get longer?
If you chose a very small PCTFREE or your data has lots of lenght-increasing updates, you might begin chaining every row to do this as an update.
You almost certainly better to do this as a CTAS.
Create table t2 as select seq.nextval, t1.* from t1.
drop t1
rename t2 to t1.
Related
So my use case is i have to find the location of the primary key column so that i can write query like select * from my_table where ID <='00000536-37ee-471c-a8e0-3d233b8102f5'
So my table has a primary key which is varchar type and values of the column is GUID generated by an application.
Here is an example of primary key
000000bd-104e-4fd6-a791-c5422f29e1b5
0000016e-7e68-4453-b360-7ffd1627dc22
00000196-2dba-4532-8cba-1e853c466697
0000025a-cfae-41b4-b8e7-ef854d49e54a
00000260-8bdb-4b30-acdb-5a67efd4dbfe
00000366-552d-48a0-b8a1-20190ccd087c
000003f2-d6d8-4a51-96cc-407063bc568b
000003ff-3d16-4e88-9cf3-bcdf01c39a2b
00000487-1e6c-4d6d-a683-6f11d517962c
000004cc-6359-4a9a-aa2a-70a6b73a06b1
00000536-37ee-471c-a8e0-3d233b8102f5
Now i need to use this table in aws DMS which accepts only query like select * from table where column =,<=,>=
My use case is to find the exact location of the millions of GUID so that i can divide table into multiple query and select based on GUID .
For example if we have 100th GID is 00000536-37ee-471c-a8e0-3d233b8102f5 then i can write query like select * from my table where GUID <=100
The limitation is i can not add any new columns in the existing table because application impact is huge .
How can i do this ?
One Option that i thought but wanted to confirm is below
Create a temp table
Temp table will have auto generated sequence and ID column
Inset into temp table select only GUID from main table with order of GUID .
In this case the value will be stored on order and i an first select GUID based on 100th number and then i can pass that GUID and write my oroginal query
But i am not sure whether this will work on not
Can some one suggest on this or suggest some other option ?
So let me explain what i want .
I want DMS to read may main table in parallel and migrate .
So lets say one DMS task can read nd migrate from 1 to 100,another 100 to 200 another >200 like that .
Currently i can not do because we dont know the position of the primary key and write the query .
If you want to divide your table into chunks of equal sizes, I would take advantage of the hexadecimal nature of the GUIDs. It will be 256 instead of 100 chunks, but this might be acceptable.
CREATE TABLE t (pk VARCHAR2(36) PRIMARY KEY);
INSERT INTO t VALUES ('000000bd-104e-4fd6-a791-c5422f29e1b5');
The easiest option would be
SELECT * FROM t WHERE pk LIKE '%b5';
A bit more advanced:
SELECT pk, to_number(substr(pk, -2),'xx') FROM t;
If you have millions of rows, this is probably faster:
ALTER TABLE t ADD (mycol GENERATED ALWAYS AS (to_number(substr(pk, -2),'xx')));
CREATE INDEX i ON t(mycol);
SELECT * FROM t WHERE mycol=181;
Once your migration is done, you can undo the additional virtual column:
DROP INDEX i;
ALTER TABLE t DROP (mycol);
I have a datamart with 5 dimension table and a fact table.
I'm trying to clean a dimension table that has few rows (4000 rows). But, the fact table have millions rows (25GB)(Indexes and partitions).
When I try to delete a row in the table dimension, the process becomes very slow. It's just as slow despite the absence of relationship with a row in the fact table (cascade delete).
Is there any way to optimize this?. Thanks in advance.
Presumably, there is a cascading delete of some sort between the dimension table and the fact table.
Adding an index on the key column in the fact table may be sufficient. Then Oracle can immediately tell if/where any given value is.
If that doesn't work, drop the foreign key constraint altogether. Delete the unused values and add the constraint back in.
You could try these strategies as well :
create another copy of the fact table but, without the dim foreign key column of the table to be cleaned.
create fact_table_new as
select dim1_k, dim2_k, dim3_k, dim4_k, dim5_k (not this column), fact_1, fact_2, ...
from fact_table ;
or
update fact_table
set dim5_fk_col = null
where dim5_fk_col in (select k_col from dim5_table) ;
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
This question already has answers here:
How to create id with AUTO_INCREMENT on Oracle?
(18 answers)
Closed 7 years ago.
I want to add a new auto increment primary column to a existing table which has data. How do I do that?
I first added a column and then try to add a sequence after that, I lost how to insert and make that column as primary key.
Say your table is called t1 and your primary-key is called id
First, create the sequence:
create sequence t1_seq start with 1 increment by 1 nomaxvalue;
Then create a trigger that increments upon insert:
create trigger t1_trigger
before insert on t1
for each row
begin
select t1_seq.nextval into :new.id from dual;
end;
If you have the column and the sequence, you first need to populate a new key for all the existing rows. Assuming you don't care which key is assigned to which row
UPDATE table_name
SET new_pk_column = sequence_name.nextval;
Once that's done, you can create the primary key constraint (this assumes that either there is no existing primary key constraint or that you have already dropped the existing primary key constraint)
ALTER TABLE table_name
ADD CONSTRAINT pk_table_name PRIMARY KEY( new_pk_column )
If you want to generate the key automatically, you'd need to add a trigger
CREATE TRIGGER trigger_name
BEFORE INSERT ON table_name
FOR EACH ROW
BEGIN
:new.new_pk_column := sequence_name.nextval;
END;
If you are on an older version of Oracle, the syntax is a bit more cumbersome
CREATE TRIGGER trigger_name
BEFORE INSERT ON table_name
FOR EACH ROW
BEGIN
SELECT sequence_name.nextval
INTO :new.new_pk_column
FROM dual;
END;
Snagged from Oracle OTN forums
Use alter table to add column, for example:
alter table tableName add(columnName NUMBER);
Then create a sequence:
CREATE SEQUENCE SEQ_ID
START WITH 1
INCREMENT BY 1
MAXVALUE 99999999
MINVALUE 1
NOCYCLE;
and, the use update to insert values in column like this
UPDATE tableName SET columnName = seq_test_id.NEXTVAL
You can use the Oracle Data Modeler to create auto incrementing surrogate keys.
Step 1. - Create a Relational Diagram
You can first create a Logical Diagram and Engineer to create the Relational Diagram or you can straightaway create the Relational Diagram.
Add the entity (table) that required to have auto incremented PK, select the type of the PK as Integer.
Step 2. - Edit PK Column Property
Get the properties of the PK column.
You can double click the name of the column or click on the 'Properties' button.
Column Properties dialog box appears.
Select the General Tab (Default Selection for the first time).
Then select both the 'Auto Increment' and 'Identity Column' check boxes.
Step 3. - Additional Information
Additional information relating to the auto increment can be specified by selecting the 'Auto Increment' tab.
Start With
Increment By
Min Value
Max Value
Cycle
Disable Cache
Order
Sequence Name
Trigger Name
Generate Trigger
It is usually a good idea to mention the sequence name, so that it will be useful in PL/SQL.
Click OK (Apply) to the Column Properties dialog box.
Click OK (Apply) to the Table Properties dialog box.
Table appears in the Relational Diagram.
Hi I have a database with loads of columns and I want to insert couple of records for testing, now in order to insert something into that database I'd have to write large query .. is it possible to do something like this
INSERT INTO table (SELECT FROM table WHERE id='5') .. I try to insert the row with ID 5 but I think this will create a problem because it will try to duplicate a record, is it possible to change this ID 5 to let say 1000 then I'd be able to insert data without writing complex query and while doing so avoiding replication of data .. tnx
In PL/SQL you can do something like this:
declare
l_rec table%rowtype;
begin
select * into l_rec from table where id='5';
l_rec.id := 1000;
insert into table values l_rec;
end;
If you have a trigger on the table to handle the primary key from a sequence (:NEW.id = seq_sequence.NEXTVAL) then you should be able to do:
INSERT INTO table
(SELECT columns_needed FROM table WHERE whatever)
This will allow you to add in many rows at one (the number being limited by the WHERE clause). You'll need to select the columns that are required by the table to be not null or not having default values. Beware of any unique constraints as well.
Otherwise you'll be looking at PL/SQL or some other form of script to insert multiple rows.
For each column that has no default value or you want to insert the values other than default, you will need to provide the explicit name and value.
You only can use an implicit list (*) if you want to select all columns and insert them as they are.
Since you are changing the PRIMARY KEY, you need to enumerate.
However, you can create a before update trigger and change the value of the PRIMARY KEY in this trigger.
Note that the trigger cannot reference the table itself, so you will need to provide some other way to get the unique number (like a sequence):
CREATE TRIGGER trg_mytable_bi BEFORE INSERT ON mytable FOR EACH ROW
BEGIN
:NEW.id := s_mytable.nextval;
END;
This way you can use the asterisk but it will always replace the value of the PRIMARY KEY.