oracle primary key settings

The primary key of Oracle database is a key technology that can ensure the integrity and consistency of data. When designing a database, setting primary keys is crucial. This article will introduce in detail the setting method of Oracle primary key and related matters.

1. What is the primary key?

The primary key is the most basic constraint in a data table, used to uniquely identify a record. The primary key must meet the following conditions:

1. Uniqueness: The primary key value must be unique in the entire data table.
2. Non-empty: The primary key value cannot be empty.
3. Permanence: The primary key value cannot be changed or deleted.

The primary key can consist of a single column or multiple columns. When using multiple columns to form a primary key, the combination of these columns must be unique.

2. Primary key setting method

In Oracle database, you can use the following two methods to set the primary key:

1. Set the primary key when creating the table

When creating a table, you can use the CREATE TABLE statement to set the primary key, for example:

CREATE TABLE employee (
emp_id NUMBER(10) PRIMARY KEY,
emp_name VARCHAR2(50) NOT NULL,
salary NUMBER(10,2) DEFAULT 0
);

In this example, the emp_id column is used as the primary key, and its data type is NUMBER(10). Use the PRIMARY KEY keyword to set this column as the primary key. At the same time, the emp_name column is set to NOT NULL, indicating that the column cannot be empty.

2. Modify the table structure and add a primary key

If the data table has been created, you can use the ALTER TABLE statement to add a primary key, for example:

ALTER TABLE employee ADD CONSTRAINT pk_employee PRIMARY KEY (emp_id);

In this example, the CREATE TABLE statement creates the employee table, but does not set the primary key. Use ALTER TABLE statement here to add primary key. First use the ADD CONSTRAINT keyword, then specify the name of the primary key constraint as pk_employee, and finally specify the primary key column emp_id in parentheses.

3. Precautions for primary key setting

When designing the database, you need to pay attention to the following matters:

1. Primary key design ideas

When setting the primary key, you need to consider business needs and determine what column or combination of columns uniquely identifies a record. It is necessary to distinguish between the unique column and the primary key in the data table. Sometimes the unique constraint is not suitable as the primary key.

2. Primary key length

The primary key is used to uniquely identify a record. When the primary key column in the data table is too long, query efficiency will be reduced, and even the performance of the entire database will be affected. Therefore, try to use shorter columns as primary keys.

3. Primary key data type

The primary key must use a unique data type. When using an integer type as the primary key, you need to pay attention to the maximum value of the primary key column to avoid the primary key value exceeding the representation range of the integer type. When using the string type as the primary key, you need to consider the difference in character sets to avoid conflicts in primary key values ​​due to different character sets.

4. Primary key auto-increment

The primary key column can use auto-increment, allowing the database to automatically generate a unique primary key value for each record. This method is also called automatic numbering. In Oracle database, you can use Sequence to achieve self-growth.

5. Foreign key association

In a relational database, the primary key of one table can be used as the foreign key of another table. When adding or modifying data, the database will automatically check whether the foreign key corresponds to the primary key to ensure data integrity. Therefore, you need to pay attention to foreign key associations when designing data tables.

4. Summary

Setting the primary key is an important step to ensure data integrity and consistency. It can ensure that each record in the data table can be uniquely identified. When using Oracle database, we can use the CREATE TABLE statement or ALTER TABLE statement to set the primary key. At the same time, you need to pay attention to issues such as the length of the primary key, data type, auto-increment, and foreign key association to ensure that the database can work efficiently.

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