I am having an issue while executing a procedure. When I am executing my procedure, it is not returning any answer. I know that there is some fault in my procedure, but I am not able to figure it out, so please help me in creating a new procedure.
Before showing my code, let me tell you why did I create the procedure:
I am actually working on my project 'Supermarket Billing management system' in that, I have already created a few tables among them, one is the Products table in which, I have created the FINAL_TOTAL column as the procedure, Now I want the procedure to calculate the total price of all the products price purchased by one single person. For instance, when you go to a Supermarket or any shopping center then, after buying few items they give a bill, and at the below of the bill, there's is a final amount which you have to pay.
So, for this reason, I have created the procedure. If you know the problem with my code then, please let me know!!
CODE:
Procedure
create procedure FINAL_TOTAL(C IN NUMBER, T OUT NUMBER)
IS
BEGIN
UPDATE Products
SET FinalTotal = FinalTotal + Total
WHERE ProdCustId = C;
Commit;
SELECT FinalTotal into T FROM Products WHERE ProdCustId = C;
END;
/
Products table:
create table Products
( ProdId number primary key,
ProdNum number not null unique,
ProdName varchar2(15),
ProdPrice int,
ProdQuantity int,
Total int,
FinalTotal int,
ProdCustId int references Customers,
ProdOrdId int references Orders,
ProdStoreId int references Stores
);
Trigger:
CREATE TRIGGER PROD_TOTAL
AFTER INSERT ON Products
BEGIN
UPDATE Products
SET Total = ProdPrice * ProdQuantity;
END;
/
insert statement in Products table:
insert into Products(ProdID,ProdNum,ProdName,ProdPrice,ProdQuantity,ProdCustId,ProdOrdId,ProdStoreId)
values(1,1001,'Syrup',30,2,1,1,1);
Execution code of procedure:
variable K number;
SQL> EXECUTE FINAL_TOTAL(1,:K);
PL/SQL procedure successfully completed.
Output:
select * from Products;
PRODID PRODNUM PRODNAME PRODPRICE PRODQUANTITY TOTAL
---------- ---------- --------------- ---------- ------------ ----------
FINALTOTAL PRODCUSTID PRODORDID PRODSTOREID
---------- ---------- ---------- -----------
1 1001 Syrup 30 2 60
1 1 1
SQL> print :K
K
----------
So, this is my code, I don't know what's the problem with my code since I am a beginner, I don't have that much idea on the procedure, and I have to use the procedure in my project because it's mandatory, so please help me in solving this issue!!
FinalTotal is NULL. Use NVL or COALESCE:
... SET FinalTotal = NVL(FinalTotal,0) + Total
NULL plus a number is NULL.
SELECT NULL + 1 FROM DUAL; -- NULL
SELECT NVL(NULL, 0) + 1 FROM DUAL; -- 1
Related
I am working on my Project 'Supermarket Billing Management System' since I am a beginner I m facing a lot of issues while making project. Here I've already created a trigger and a procedure but I don't know how I can execute it, I've created a trigger for a total price of a single Product i.e ProdTotal = ProdPrice * ProdQuantity;.
That means whenever a user enters some data in the Products table, then this trigger must get executed, but I don't know how to execute it, similarly, I've created a procedure to calculate the total price of all the products purchased by a single customer. Just like when you go to the supermarket or any store then after purchasing the items, you get a bill and there is the final total amount. I m not even exactly sure whether my procedure code is right or wrong, though it was created successfully, I m not sure whether it will give me the exact output which I want, So if you can help me then, please let me know, I've researched a lot from different websites and also from many youtube videos but seriously I am not getting how to solve it, so please help me!
Code:
Products table
create table Products
( ProdId number primary key,
ProdNum number not null unique,
ProdName varchar2(15),
ProdPrice int,
ProdQuantity int,
ProdCustId int references Customers,
ProdOrdId int references Orders,
ProdStoreId int references Stores
);
Payments table
create table Payments
( PayId int primary key,
PayDate date,
ProdTotal int,
FinalTotal int,
PayOrdId int references orders,
PayProdId int references Products,
PayCustId int references Customers
);
Trigger code
create trigger PROD_TOTAL
AFTER INSERT ON Products
BEGIN
UPDATE Payments
SET ProdTotal = (SELECT Products.ProdPrice * Products.ProdQuantity FROM Products);
END;
/
Procedure code
create procedure FINAL_TOTAL(C IN NUMBER, T OUT NUMBER)
IS
BEGIN
UPDATE Payments
SET FinalTotal = FinalTotal + ProdTotal
WHERE PayCustId = C;
Commit;
SELECT FinalTotal into T FROM Payments WHERE PayCustId = C;
END;
/
Insert statement in Product table:
insert into Products values(1,1001,'Syrup',30,4,1,1,1);
Insert statements in Payments table:
insert into Payments(PayId, PayDate, PayOrdID, PayProdId, PayCustId)
values(1,date'2020-10-07',1,1,1);
Output:
select * from products;
PRODID PRODNUM PRODNAME PRODPRICE PRODQUANTITY PRODCUSTID
---------- ---------- --------------- ---------- ------------ ----------
PRODORDID PRODSTOREID
---------- -----------
1 1001 Syrup 30 4 1
1 1
select * from Payments;
PAYID PAYDATE PRODTOTAL FINALTOTAL PAYORDID PAYPRODID PAYCUSTID
---------- --------- ---------- ---------- ---------- ---------- ----------
1 07-OCT-20 1 1 1
Now here, as you can see PRODTOTAL and FINALTOTAL column is blank, I know why it is blank because I didn't enter any value. And the reason why I didn't enter any value in these two columns is that I want, the system should automatically calculate that calculation with the help of trigger and procedure and, I can't even remove trigger and procedure because it's mandatory in our project to use both of these concepts. So please help me!!!
As already proposed, first try to get the design right with respect to your requirements. You can implement many constraints just by designing correctly your database schema.
Stay away from triggers and PL/SQL for as long as possible. It will force you to better design in the end and will pay off.
Before using triggers for business logic, try to use views for things that can be selected. That's what the database is for.
When you are "done", test for the performance and if it's suboptimal, improve your schema. If nothing helps, start using triggers for business logic.
I've put together a sample with views I am talking about. I hope it can get you started.
create table Products (
ProdId number generated always as identity primary key
, ProdName varchar2(20) not null
);
create table Stores (
StoreId number generated always as identity primary key
, StoreName varchar2(20) not null
);
create table Customers (
CustomerId number generated always as identity primary key
, CustomerName varchar2(20) not null
);
create table Prices (
PriceId number generated always as identity primary key
, ProdId number not null
, Price number
, ValidFrom date default on null sysdate
, constraint fk_Prices_Product foreign key (ProdId) references Products (ProdId)
);
create unique index uniq_prices_product_price on Prices (ProdId, ValidFrom);
create table Orders (
OrderId number generated always as identity primary key
, CustomerId number not null
, StoreId number not null
, OrderedAt date default on null sysdate
, constraint fk_Orders_Customer foreign key (CustomerId) references Customers (CustomerId)
, constraint fk_Orders_Store foreign key (StoreId) references Stores (StoreId)
);
create table OrderLines (
OrderLineId number generated always as identity primary key
, OrderId number not null
, ProdId number not null
, ProdQuantity number not null
, constraint fk_OrderLines_Order foreign key (OrderId) references Orders (OrderId)
, constraint fk_OrderLines_Prod foreign key (ProdId) references Products (ProdId)
);
create table Payments (
PaymentId number generated always as identity primary key
, OrderId number not null
, PaidAt date default on null sysdate
, PaidAmount number not null
, constraint fk_Payments_Order foreign key (OrderId) references Orders (OrderId)
);
create view Prices_V as
select
p.*
, coalesce(
lead(p.ValidFrom) over (partition by p.ProdId order by p.ValidFrom)
, to_date('9999', 'YYYY')
) ValidTo
from Prices p;
create view Orders_V as
select
o.*
, (
select sum(ol.ProdQuantity * p.Price)
from OrderLines ol
join Prices_V p on (p.ProdId = ol.ProdId and o.OrderedAt between p.ValidFrom and p.ValidTo)
where o.OrderId = ol.OrderId
) Total
, (
select sum(PaidAmount)
from Payments p
where p.OrderId = o.OrderId
) TotalPaid
from Orders o;
insert into Products(ProdName)
select 'Prod A' from dual union all
select 'Prod B' from dual;
insert into Stores(StoreName) values ('Store A');
insert into Customers(CustomerName)
select 'Customer A' from dual union all
select 'Customer B' from dual;
insert into Prices(ProdId, Price, ValidFrom)
select 1, 10, sysdate - 10 from dual union all
select 1, 12, sysdate - 2 from dual union all
select 1, 14, sysdate + 3 from dual union all
select 2, 100, sysdate - 10 from dual union all
select 2, 90, sysdate - 2 from dual union all
select 2, null, sysdate + 5 from dual;
insert into Orders(CustomerId, StoreId, OrderedAt)
select 1 cid, 1 stoid, sysdate - 5 from dual union all
select 2, 1, sysdate - 5 from dual union all
select 2, 1, sysdate - 1 from dual;
insert into OrderLines(OrderId, ProdId, ProdQuantity)
select 1 ordid, 1 prodid, 3 prodquant from dual union all
select 1, 2, 2 from dual union all
select 2, 2, 10 from dual union all
select 3, 2, 10 from dual;
insert into Payments(OrderId, PaidAmount) values (2, 500);
select * from Prices_V order by ProdId, ValidFrom;
select * from OrderLines order by OrderId, ProdId;
select * from Orders_v order by OrderId;
Some of the ideas in there:
Prices are stored in separate table, reference the product and have validity so that product price can change over time. Price view have ValidTo column added so it's easier to work with
There is a unique index on Prices so that we cannot have 2 prices for the same product at the same time
You can have many items in order, so that's why there is Orders and OrderLines tables in 1-to-many relationship
In Order_V the total paid is shown (using a subquery on Payments) and the total order values is shown (using a subquery on OrderLines and Prices, date of order is used to get prices form the correct period)
Based on the schema you will se what things you can represent and which you cannot. It's your job to make it match your requirements :)
And now I've come to the point you say triggers and procedures are mandatory in your project. Hence I have a proposal:
Create a procedure that will allow users to create new price for a product. It should definitely check that the validity does not start in the past. Then implement another one that allows for changing the valid to date (also cannot end in the past). You can than revoke any insert/update privileges on Products table and force users to use your procedures that will contain this business logic.
Create a table PricesLog and trigger on Prices that will insert the PriceId, old.Price, new.Price, sysdate and User to the log on any inserts/updates to the prices table.
select rownum into v_rownum
from waitlist
where p_callnum=callnum
order by sysdate;
tried doing this but gives too many values.
and if I do p_snum=snum, it will keep returning 1. I need it to return 2 if it's #2 on the waitlist.
select rn into v_rownum
from (select callnum,
row_number() over (order by sysdate) rn
from waitlist)
where p_snum=snum;
Almost got it to work. Running into issues in the first select. I believe I might have to use v_count instead. Also Ordering by Sysdate even if a second apart will order it correctly.
SNU CALLNUM TIME
--- ---------- ---------
101 10125 11-DEC-18
103 10125 11-DEC-18
BTW time is = date which I entered people into waitlist using sysdate. So I suppose ordering by time could work.
create table waitlist(
snum varchar2(3),
callnum number(8),
time date,
constraint fk_waitlist_snum foreign key(snum) references students(snum),
constraint fk_waitlist_callnum foreign key(callnum) references schclasses(callnum),
primary key(snum,callnum)
);
is the waitlist table.
I used Scott's DEPT table to create your WAITLIST; department numbers represent CALLNUM column:
SQL> select * From waitlist;
CALLNUM WAITER
---------- --------------------
10 ACCOUNTING
20 RESEARCH
30 SALES
40 OPERATIONS
How to fetch data you need?
using analytic function (ROW_NUMBER) which orders values by CALLNUMs, you'll know the order
that query will be used as an inline view for the main query that returns number in the waitlist for any CALLNUM
Here's how:
SQL> select rn
2 from (select callnum,
3 row_number() over (order by callnum) rn
4 from waitlist
5 )
6 where callnum = 30;
RN
----------
3
SQL>
rownum in oracle is a generated column, it does not refer to any specific row, it is just the nth row in a set.
With a select into it can only return one row (hence the two many rows error) so rownum will always be 1.
Without more details about your table structure, and how you are uniquely identifying records it is hard to give assist you further with a solution.
The situation is that, when I import a file into the database, one of the first thing I usually do is to assign an unique ID for each record.
I normally do below in TSQL
ALTER TABLE MyTable
ADD ID INT IDENTITY(1,1)
I am wondering if there is something similar in PL SQL?
All my search result come back with multiple steps.
Then I'd like to know what PL SQL programmer typically do to ID records after importing a file. Do they do that?
The main purpose for me to ID these records is to trace it back after manipulation/copying.
Again, I understand there is solution there, my further question is whether PL SQL programmer actually do that, or there is other alternative which making this step not necessary in PL SQL?
OK then, as you're on Oracle 11g, there's no identity column there so - back to multiple steps. Here's an example:
I'm creating a table that simulates your imported table:
SQL> create table tab_import as
2 select ename, job, sal
3 from emp
4 where deptno = 10;
Table created.
Add the ID column:
SQL> alter table tab_import add id number;
Table altered.
Create a sequence which will be used to populate the ID column:
SQL> create sequence seq_imp;
Sequence created.
Update current rows:
SQL> update tab_import set
2 id = seq_imp.nextval;
3 rows updated.
Create a trigger which will take care about future inserts (if any):
SQL> create or replace trigger trg_bi_imp
2 before insert on tab_import
3 for each row
4 begin
5 :new.id := seq_imp.nextval;
6 end;
7 /
Trigger created.
Check what's in the table at the moment:
SQL> select * from tab_import;
ENAME JOB SAL ID
---------- --------- ---------- ----------
CLARK MANAGER 2450 1
KING PRESIDENT 5000 2
MILLER CLERK 1300 3
Let's import some more rows:
SQL> insert into tab_import (ename, job, sal)
2 select ename, job, sal
3 from emp
4 where deptno = 20;
3 rows created.
The trigger had silently populated the ID column:
SQL> select * From tab_import;
ENAME JOB SAL ID
---------- --------- ---------- ----------
CLARK MANAGER 2450 1
KING PRESIDENT 5000 2
MILLER CLERK 1300 3
SMITH CLERK 800 4
JONES MANAGER 2975 5
FORD ANALYST 3000 6
6 rows selected.
SQL>
Shortly: you need to
alter table and add the ID column
create a sequence
create a trigger
The end.
The answer given by #Littlefoot would be my recommendation too - but still I thought I could mention the following variant which will work only if you do not intend to add more rows to the table later.
ALTER TABLE MyTable add id number(38,0);
update MyTable set id = rownum;
commit;
My test:
SQL> create table tst as select * from all_tables;
Table created.
SQL> alter table tst add id number(38,0);
Table altered.
SQL> update tst set id = rownum;
3815 rows updated.
SQL> alter table tst add constraint tstPk primary key (id);
Table altered.
SQL>
SQL> select id from tst where id < 15;
ID
----------
1
2
3
4
5
6
7
8
9
10
11
ID
----------
12
13
14
14 rows selected.
But as mentioned initially,- this only fixes numbering for the rows you have at the time of the update - your'e not going to get new id values for new rows anytime later - if you need that, go for the sequence solution.
You can add an id column to a table with a single statement (Oracle 11g, see dbfiddle):
alter table test_
add id raw( 16 ) default sys_guid() ;
Example:
-- create a table without an id column
create table test_ ( str )
as
select dbms_random.string( 'x', 16 )
from dual
connect by level <= 10 ;
select * from test_ ;
STR
ULWL9EXFG6CIO72Z
QOM0W1R9IJ2ZD3DW
YQWAP4HZNQ57C2UH
EETF2AXD4ZKNIBBF
W9SECJYDER793MQW
alter table test_
add id raw( 16 ) default sys_guid() ;
select * from test_ ;
STR ID
ULWL9EXFG6CIO72Z 0x782C6EBCAE2D7B9FE050A00A02005D65
QOM0W1R9IJ2ZD3DW 0x782C6EBCAE2E7B9FE050A00A02005D65
YQWAP4HZNQ57C2UH 0x782C6EBCAE2F7B9FE050A00A02005D65
EETF2AXD4ZKNIBBF 0x782C6EBCAE307B9FE050A00A02005D65
W9SECJYDER793MQW 0x782C6EBCAE317B9FE050A00A02005D65
Testing
-- Are the id values unique and not null? Yes.
alter table test_
add constraint pkey_test_ primary key ( id ) ;
-- When we insert more rows, will the id be generated? Yes.
begin
for i in 1 .. 100
loop
insert into test_ (str) values ( 'str' || to_char( i ) ) ;
end loop ;
end ;
/
select * from test_ order by id desc ;
-- last 10 rows of the result
STR ID
str100 0x782C806E16A5E998E050A00A02005D81
str99 0x782C806E16A4E998E050A00A02005D81
str98 0x782C806E16A3E998E050A00A02005D81
str97 0x782C806E16A2E998E050A00A02005D81
str96 0x782C806E16A1E998E050A00A02005D81
str95 0x782C806E16A0E998E050A00A02005D81
str94 0x782C806E169FE998E050A00A02005D81
str93 0x782C806E169EE998E050A00A02005D81
str92 0x782C806E169DE998E050A00A02005D81
str91 0x782C806E169CE998E050A00A02005D81
Regarding your other questions:
{1} Then I'd like to know what PL SQL programmer typically do to ID records after importing a file. Do they do that? The main purpose for me to ID these records is to trace it back after manipulation/copying.
-> As you know, the purpose of an id is: to identify a row. We don't "do anything to IDs". Thus, your usage of IDs seems legit.
{2} Again, I understand there is solution there, my further question is whether PL SQL programmer actually do that, or there is other alternative which making this step not necessary in PL SQL?
-> Not quite sure what you are asking here. Although there is a ROWID() pseudocolumn (see documentation), we should not use it to identify rows.
"You should not use ROWID as the primary key of a table. If you delete
and reinsert a row with the Import and Export utilities, for example,
then its rowid may change. If you delete a row, then Oracle may
reassign its rowid to a new row inserted later."
I was trying to set up a simple trigger when something is deleted from enrolls it also deletes from scores and student tables. I feel like I have set everything up properly, but I keep getting this error: error ora-00922: missing or invalid operation. I have done some research into the error, but I am not getting anywhere with. I am doing this in sql developer. I am semi new to sql so any help would be greatly appreciated. My code is below:
delimiter //
create or replace TRIGGER enrolls_trigger
AFTER DELETE ON ENROLLS
FOR EACH ROW
BEGIN
DELETE FROM scores
WHERE scores.sid= old.sid
AND scores.term = old.term AND scores.lineno = old.lineno
AND scores.compname = old.compname AND scores.points = old.points;
DELETE FROM students
WHERE students.sid = old.sid;
END//
Your syntax is a bit off. To reference the previous value of a DML transaction, you use :old.
-- delimiter
CREATE OR REPLACE TRIGGER enrolls_trigger AFTER
DELETE ON enrolls
FOR EACH ROW
BEGIN
DELETE FROM scores
WHERE
scores.sid =:old.sid
AND scores.term =:old.term
AND scores.lineno =:old.lineno
AND scores.compname =:old.compname
AND scores.points =:old.points;
DELETE FROM students
WHERE
students.sid =:old.sid;
END;
--delimiter
Also, if you're using SQL Developer, you'll want to have an ';' after your END keyword on the trigger body.
Trigger Docs
For better help going forward, include your TABLE DDL. I created these for ease of use.
CREATE TABLE enrolls (
sid INTEGER,
term INTEGER,
lineno INTEGER,
compname VARCHAR2(10),
points INTEGER
);
CREATE TABLE scores (
sid INTEGER,
term INTEGER,
compname VARCHAR2(10),
points INTEGER,
lineno INTEGER
);
CREATE TABLE students (
sid INTEGER
);
I'd suggest another approach - foreign key constraints created with the ON DELETE CASCADE option. Have a look at the following example.
Thanks to Jeff who provided CREATE TABLE statements which I've slightly modified, i.e. added only necessary constraints. Note that I've chosen only the SID column to be a foreign key from the SCORES table to ENROLLS. BTW, what's the point in repeating that many columns in the SCORES table? I'd suggest you to keep only the foreign key constraint column (such as SID), and omit the others.
Finally, here we go: Create tables:
SQL> CREATE TABLE enrolls (
2 sid INTEGER constraint pk_en primary key,
3 term INTEGER,
4 lineno INTEGER,
5 compname VARCHAR2(10),
6 points INTEGER
7 );
Table created.
SQL> CREATE TABLE scores (
2 sid INTEGER,
3 term INTEGER,
4 lineno INTEGER,
5 compname VARCHAR2(10),
6 points INTEGER,
7 constraint fk_sco_en foreign key (sid)
8 references enrolls
9 on delete cascade
10 );
Table created.
SQL> CREATE TABLE students (
2 sid INTEGER,
3 constraint fk_stu_en foreign key (sid)
4 references enrolls
5 on delete cascade
6 );
Table created.
SQL>
Insert sample data:
SQL> insert into enrolls (sid, term) values (100, 1);
1 row created.
SQL> insert into enrolls (sid, term) values (200, 2);
1 row created.
SQL> insert into scores (sid, term) values (100, 1);
1 row created.
SQL> insert into scores (sid, term) values (200, 2);
1 row created.
SQL> insert into students (sid) values (100);
1 row created.
SQL> insert into students (sid) values (200);
1 row created.
SQL>
SQL> select * From students;
SID
----------
100
200
SQL> select * From scores;
SID TERM LINENO COMPNAME POINTS
---------- ---------- ---------- ---------- ----------
100 1
200 2
SQL> select * From enrolls;
SID TERM LINENO COMPNAME POINTS
---------- ---------- ---------- ---------- ----------
100 1
200 2
SQL>
Now: if I delete a row from the ENROLLS table, Oracle will do the rest:
SQL> delete from enrolls where sid = 100;
1 row deleted.
SQL> select * From students;
SID
----------
200
SQL> select * From scores;
SID TERM LINENO COMPNAME POINTS
---------- ---------- ---------- ---------- ----------
200 2
SQL> select * From enrolls;
SID TERM LINENO COMPNAME POINTS
---------- ---------- ---------- ---------- ----------
200 2
SQL>
See? SID = 100 has been deleted from all tables, without any additional coding (i.e. no triggers needed).
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.
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
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
Try this:
create sequence seq_EmpID start with 1 increment by 1
insert into Emp_Table values(seq_EmpID.nextval,'Ram')
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.
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;
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
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>