How to create and manage fields in Oracle database

A field in Oracle database refers to each column in the table. In Oracle database, we can create and manage fields in many ways. In this article, we will detail how to create and manage fields in Oracle Database.

1. Create a table

In Oracle database, to create a new table, we need to use the CREATE TABLE statement. For example, to create a table named "employees" we can use the following statement:

CREATE TABLE employees (
employee_id INT PRIMARY KEY,
first_name VARCHAR(50),
last_name VARCHAR(50),
email VARCHAR(100),
hire_date DATE,
salary INT,
department_id INT
);

In this example, we create A table named "employees" contains seven fields. Let's take a closer look at these fields.

1. employee_id

This is an INT type field used to store the employee's ID. This field is designated as PRIMARY KEY, which means it will serve as the primary key for the table.

2. first_name

This is a VARCHAR(50) type field used to store the employee's name.

3. last_name

This is a VARCHAR(50) type field used to store the employee's last name.

4. email

This is a VARCHAR(100) type field used to store the employee's email address.

5. hire_date

This is a DATE type field used to store the date the employee joined the company.

6. salary

This is an INT type field used to store the employee's salary.

7. department_id

This is an INT type field used to store the ID of the department where the employee works.

2. Add fields

In some cases, we may need to add new fields to the table. In Oracle database, we can use ALTER TABLE statement to add new fields. For example, to add a new field named "phone_number" to the "employees" table above, we can use the following statement:

ALTER TABLE employees ADD phone_number VARCHAR(20);

In this example, we use the ALTER TABLE statement to add a new field called "phone_number" to the "employees" table. This field is a VARCHAR(20) type field that stores the employee's phone number.

3. Modify fields

In some cases, we may need to modify the fields that already exist in the form. In Oracle database, we can use ALTER TABLE statement to modify existing fields. For example, to add a DEFAULT value to the "salary" field in the "employees" table above, we can use the following statement:

ALTER TABLE employees MODIFY salary INT DEFAULT 0;

In this In the example, we use the ALTER TABLE statement to modify the "salary" field in the "employees" table. We changed the field's type to INT and gave it a default value of 0.

4. Delete fields

In some cases, we may need to delete one or more fields from the table. In Oracle database, we can use ALTER TABLE statement to delete existing fields. For example, to delete the "phone_number" field from the "employees" table above, we can use the following statement:

ALTER TABLE employees DROP COLUMN phone_number;

In this example, we use ALTER The TABLE statement deletes the "phone_number" field from the "employees" table.

Summary

In Oracle database, we can use statements such as CREATE TABLE, ALTER TABLE and DROP TABLE to create and manage tables. A field is each column in a table, and we can add, modify, or delete fields using the ALTER TABLE statement. These features are useful for applications that require frequent table and field management.

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