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.
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oracle
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;
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.
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.
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
Source: Stackoverflow.com