Auto Increment for Oracle - oracle

Question

I need to create a sequence and a trigger to auto-increment the primary key on a table but I have no idea on how to do it.

Answer 1

Create the table and the sequence
SQL> create table staff (
2 emp_id number primary key,
3 staff_name varchar2(100)
4 );
Table created.
SQL> create sequence emp_id_seq;
Sequence created.
Now, you can create a trigger that uses the sequence to populate the primary key
SQL> create trigger trg_emp_id
2 before insert on staff
3 for each row
4 begin
5 select emp_id_seq.nextval
6 into :new.emp_id
7 from dual;
8 end;
9 /
Trigger created.
Now, when you insert data, you woon't need to specify the EMP_ID column-- it will automatically be populated by the trigger
SQL> insert into staff( staff_name ) values ('Justin');
1 row created.
SQL> select * from staff;
EMP_ID STAFF_NAME
---------- --------------------
1 Justin

Answer 2

Read this, Beautiful article.
how sequence [auto increment in oracle]
syntax
Create sequence sequence_name
start with value
increment by value
minvalue value
maxvalue value;
example
SQL> create table emp (
emp_id number(10),
fname varchar2(25),
lname varchar2(25),
constraint pk_emp_id PRIMARY KEY(emp_id)
);
SQL> Create sequence emp_sequence
start with 1
increment by 1
minvalue 1
maxvalue 10000;
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Darvin','Johnson');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Mig','Andrews');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Alex','Martin');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Jon','paul');
SQL> insert into emp (emp_id,fname,lname) values(emp_sequence.nextval,'Yatin','Bones');
in emp_sequence.nextval where emp_sequence is the name of sequence we created above and nextval is a function that is used to assign the next number from emp_sequence to emp_id column in emp table.
SQL> select * from emp;
EMP_ID FNAME LNAME
---------- ------------------------- -------------------------
1 Darvin Johnson
2 Mig Andrews
3 Alex Martin
4 Jon paul
5 Yatin Bones

Answer 3

Try this:
create sequence seq_EmpID start with 1 increment by 1
insert into Emp_Table values(seq_EmpID.nextval,'Ram')

Answer 4

I am not sure which version of Oracle you are using, but the following will work in 19c:
create table staff (
emp_id NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY PRIMARY KEY,
staff_name varchar2(100)
);
https://docs.oracle.com/en/database/other-databases/nosql-database/19.3/java-driver-table/creating-tables-identity-column.html
The command above creates a system sequence that is automatically employed to populate the key value. you cannot drop the sequence created as it is a system sequence, but because of the dependency on the column when the table is dropped and the recycle bin purged it is removed.

Answer 5

Very good question!!
Probably sequence can be used in this way - also, I am not sure if there really is a difference :
CREATE SEQUENCE emp_id_seq MINVALUE 1 START WITH 1 INCREMENT BY 1 CACHE 10;

Answer 6

First creating the table :
sql-> create table item(id int primary key, name varchar(25),qty int, price int);
Now we want to make auto increment sequence to the first column i.e. id
sql-> CREATE SEQUENCE id MINVALUE 1 START WITH 1 CACHE 10; //system saves the last 10 items in temp memory
This will create auto increment.
Now we are inserting data:
sql-> insert into item VALUES(id.nextval,'ddcd',2,4);
sql-> insert into item VALUES(id.nextval,'ddcd',676,4);
Finally Displaying the table :
SQL> select * from item;
ID NAME QTY PRICE
1 ddcd 2 4
2 ddcd 676 4

Answer 7

If you use a sequence for several tables, because the value of the sequence is inconsistent example:
we have two tables emp and depeartement:
If I use the sequence on emp I would have: ID_dept = 6 because the 5 is already used in the other table.
example :
SQL> insert into emp values(masequence.nextval,'aaa');
1 ligne crÚÚe.
SQL> insert into departement values(masequence.nextval,'aaa');
1 ligne crÚÚe.
SQL> select * from emp;
ID_EMP NOM_EMP
---------- -------------------------
5 aaa
SQL> select * from departement;
ID_DEPT NOM_DEPT
---------- ----------
6 aaa
SQL>