I wonder if there is a way to create a table column with an primary key which is auto incremented without using a sequence.
I saw that it was working by using IDENTITY on Microsofts SQL Server and AUTO_INCREMENT on MySQL, but cannot get something that works with Oracle DB.
This is my current approach:
CREATE TABLE test
( id NUMBER(6) IDENTITY,
CONSTRAINT pk_id PRIMARY KEY (id)
)
Identity columns in Oracle would meet your requirement, but they were introduced in Oracle Database 12c.
Since you are on Oracle Database 11g, the best approach would be to use a sequence + trigger approach. Tim Hall has a good write up of this here:
Excerpt:
Create a table with a suitable primary key column and a sequence to
support it.
CREATE TABLE departments (
ID NUMBER(10) NOT NULL,
DESCRIPTION VARCHAR2(50) NOT NULL);
ALTER TABLE departments ADD (
CONSTRAINT dept_pk PRIMARY KEY (ID));
CREATE SEQUENCE dept_seq;
Create a trigger to populate the ID column if it's not specified in
the insert.
CREATE OR REPLACE TRIGGER dept_bir
BEFORE INSERT ON departments
FOR EACH ROW
WHEN (new.id IS NULL)
BEGIN
SELECT dept_seq.NEXTVAL
INTO :new.id
FROM dual;
END;
Related
I have written an application in Javascript which inserts data into two tables via a connection to a MariaDB server.
There should be a 1:1 correspondance between the rows in these tables when first running the application.
One table stores (simulated) data about properties, the other table stores data about prices. There should be 1 price for each property. At a later date, the price might change, so there could be more than one entry for the price, but this cannot happen when the application is first run. These entries also cannot be in violation of a unique index - but they are.
Perhaps I have misconfigured something in MariaDB? Here is the code which generates the tables.
drop table if exists property_price;
drop table if exists property;
create table property
(
unique_id bigint unsigned not null auto_increment primary key,
web_id bigint unsigned not null,
url varchar(256),
street_address varchar(256),
address_country varchar(64),
property_type varchar(64),
num_bedrooms int,
num_bathrooms int,
created_datetime datetime not null,
modified_datetime datetime not null
);
create table property_price
(
property_unique_id bigint unsigned not null,
price_value decimal(19,2) not null,
price_currency varchar(64) not null,
price_qualifier varchar(64),
added_reduced_ind varchar(64),
added_reduced_date date,
created_datetime datetime not null
);
alter table property_price
add constraint fk_property_unique_id foreign key(property_unique_id)
references property(unique_id);
alter table property
add constraint ui_property_web_id
unique (web_id);
alter table property
add constraint ui_url
unique (url);
alter table property_price
add constraint ui_property_price
unique (property_unique_id, price_value, price_currency, price_qualifier, added_reduced_ind, added_reduced_date);
Below is a screenshot from DBeaver showing that a select statement returns two identical rows.
I don't understand why the unique constraint appears to be violated. The constraint does sometimes work, because if I run my application again, it fails because it attempts to insert a duplicate row which already exists in the DB. (Not the same as the one shown below.)
Can anyone point me in the right direction as to how I might debug this?
MariaDB permits multiple values on columns which form part of a unique constraint.
My solution would be to put the logic for checking for duplicate rows into the application, rather than this being on the database side. Essentially this means the unique constraint is not being used.
I need that the values for a ColumnID, which is a Primary Key, to start at 100 and increment by 5. This condition is asked to be included as a constraint before populating the tables. I already created the tables, I just need to add that constraint. I know I can't use AUTO_INCREMENT because the increase is only by 1. Is there a way to do it in MySQL?
MySQL does not provide any built-in function to create a sequence for a table's rows or columns. But we can generate it via SQL query.
Example:
Let us understand it with the help of the following example. First, we need to create a new table and make sure that there is one column with the AUTO_INCREMENT attribute and that too, as PRIMARY KEY.
Execute the below query to create a table:
CREATE TABLE Insects (
Id INT AUTO_INCREMENT PRIMARY KEY,
Name VARCHAR(30) NOT NULL,
Type VARCHAR(30) NOT NULL,
Origin VARCHAR(30) NOT NULL
);
Then you can alter your column to start from another value:
ALTER TABLE Insects AUTO_INCREMENT=100;
You can check it here.
I have a main table called results. E.g.
CREATE TABLE results (
r_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
r_date DATE NOT NULL,
system_id INT NOT NULL,
FOREIGN KEY (system_id) REFERENCES systems(s_id) ON UPDATE CASCADE ON DELETE CASCADE
);
The systems table as:
CREATE TABLE systems (
s_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
system_name VARCHAR(50) NOT NULL UNIQUE
);
I'm writing a program in Python with MySQL connector. Is there a way to add data to the systems table and then auto assign the generated s_id to the results table?
I know I could INSERT into systems, then do another call to that table to see what the ID is for the s_name, to add to the results table but I thought there might be quirk in SQL that I'm not aware of to make life easier with less calls to the DB?
You could do what you describe in a trigger like this:
CREATE TRIGGER t AFTER INSERT ON systems
FOR EACH ROW
INSERT INTO results SET r_date = NOW(), system_id = NEW.s_id;
This is possible only because the columns of your results table are easy to fill in from the data the trigger has access to. The auto-increment fills itself in, and no additional columns need to be filled in. If you had more columns in the results table, this would be harder.
You should read more about triggers:
https://dev.mysql.com/doc/refman/8.0/en/create-trigger.html
https://dev.mysql.com/doc/refman/8.0/en/triggers.html
I have a database table with several columns where some of them used to form the primary key together. Now the model changed and a single primary key column, called 'id', gets introduced.
When I alter the table and add the column, the column gets populated in every row with an default value, 0 or NULL, so that it can not be used as a candidate for a new primary key. To achieve that, I have to have a different (numerical) value for 'id' in every row. How can I achieve that, preferably as generic as possible (MySQL, Oracle, SQL Server).
Here is a sample of how to add an identity column that populates as a primary key.
create table #t (vals varchar(100))
insert into #t
values('a'),('b'),('c')
alter table #t
add ID int identity primary key
select * from #t
Results:
vals ID
a 1
b 2
c 3
This is a SQL Server answer. I don't know how the other databases work.
CREATE TABLE Persons (
ID int IDENTITY(1,1) PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
Might be this will be helpful.
The MS SQL Server uses the IDENTITY keyword to perform an auto-increment feature.
In the example above, the starting value for IDENTITY is 1, and it will increment by 1 for each new record.
Tip: To specify that the "ID" column should start at value 10 and increment by 5, change it to IDENTITY(10,5).
To insert a new record into the "Persons" table, we will NOT have to specify a value for the "ID" column (a unique value will be added automatically):
I have an existing product table which is already populated with 120 records and I have tried below SQL query:
ALTER TABLE product ADD product_id
INT PRIMARY KEY AUTO_INCREMENT
But it's given me the error:
Error: #1075 - Incorrect table definition; there can be only one auto column and it must be defined as a key
Here is work around
create a simple column with autoincrement
browse the table and again make this newly added column as primary key
You are done !
:) Thanks to Guy who is not in Stackoverflow
Friend
If you try to do this in MSSQL then your script will be this.
suppose your table is below
create table product
(
name varchar(20),
product_type varchar(20)
)
and suppose you entered some record in this table after that you want to add a column that name product_id with auto increment and primary key. Then you use this script that is below
alter table product add product_ID int primary key identity(1,1)
suppose this will be help full for you.
There can only be one auto increment field per table. But, you could have a calculated field based on the auto increment field. Or, you could have an int field where you manage the sequence by front end code or by a trigger. And also you could use a sequence in SQL Server.
CREATE SEQUENCE MySequence START WITH 100;
CREATE TABLE MyTable
(
RealIdentity INT IDENTITY(1,1),
RandomCol NVARCHAR(100),
FakeIdentity INT DEFAULT NEXT VALUE FOR MySequence
);
UPDATE - MySQL Way
I just noticed that your question is taged for MySQL. Above answer is for MS SQL. Here's how you'd do the same in MySQL.
How do I create a sequence in MySQL?
MySQL equivalent of Oracle's SEQUENCE.NEXTVAL