oracle settings auto-increment

Oracle database is a powerful and widely used relational database management system that supports the use of auto-increment (auto-increment) functions in tables. When we design a database, we usually need to set an auto-increment field as the primary key of the table to ensure the uniqueness of the table. In this article, we will introduce how to set up auto-increment fields in Oracle database.

1. Create table

In Oracle database, you can create a data table through the CREATE TABLE statement. The following is an example of creating a table:

CREATE TABLE student (
id NUMBER(10),
name VARCHAR2(50),
age NUMBER(2)
);

In the above example, we created a table named student, which contains three fields: id, name, and age. Among them, the data type of the id field is NUMBER and the length is 10, which means it can store 10 digits.

2. Set the primary key

When creating a table, it is very important to set the primary key. The primary key is used to uniquely identify each record in the table and is an important part of every table. In Oracle database, you can use the CONSTRAINT statement to set the primary key, as follows:

CREATE TABLE student (
id NUMBER(10) PRIMARY KEY,
name VARCHAR2(50),
age NUMBER(2)
);

In the above example, we set the id field as the primary key. The primary key is unique and required, and each record must have a primary key.

3. Use Sequence to automatically increment

In Oracle database, you can use Sequence to automatically increment the value of the primary key field. To use Sequence, you need to create a Sequence first, as follows:

CREATE SEQUENCE student_id_seq
INCREMENT BY 1
START WITH 1
MAXVALUE 9999999999
MINVALUE 1
CACHE 20;

In the above example, we created a Sequence named student_id_seq, which will automatically increase from 1, with a maximum value of 9999999999, a minimum value of 1, and cache 20 numbers each time.

Next, we can associate the Sequence with the primary key of the table and use it as the default value of the primary key, as follows:

CREATE TABLE student (
id NUMBER(10 ) DEFAULT student_id_seq.NEXTVAL PRIMARY KEY,
name VARCHAR2(50),
age NUMBER(2)
);

In the above example, we use the NEXTVAL of the student_id_seq sequence as the id field The default value, so that every time a record is inserted, the value of the id field will be automatically incremented to ensure the uniqueness of the data.

4. Use triggers to automatically increment

In addition to using Sequence to automatically increment, you can also use triggers to automatically increment the value of the primary key field. With triggers, you can automatically get the next available primary key value when inserting a record and insert it into the table.

The following is an example of using a trigger to add an auto-increment feature:

CREATE TRIGGER student_bir
BEFORE INSERT ON student
FOR EACH ROW
BEGIN
SELECT student_id_seq. NEXTVAL
INTO :new.id
FROM dual;
END;

In the above example, we created a trigger named student_bir. Each time before inserting a record, Get the next available primary key value from the student_id_seq sequence and assign it to the id field.

Summary:

In Oracle database, automatically incrementing primary key fields can be achieved through Sequence and triggers. Using Sequence can implement the auto-increment feature more concisely and conveniently, while using triggers can more flexibly control the generation method of primary key fields.

No matter which method is used, automatically incrementing the primary key can improve the uniqueness and readability of the data, while also saving the time and energy of manually entering the primary key. This has very wide applications in real database applications.

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