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This article is about understanding what primary keys, foreign keys, and indexes are in the database. The editor thought it was very practical, so I shared it with you as a reference. Let's follow the editor and have a look.

The primary key in the database refers to the attribute or group of attributes that can uniquely identify a record, the foreign key means that the primary key in another table acts as a connection with other tables, and the index is used to quickly find records with specific values.

Primary key in the database

A primary key in a database refers to a property or group of attributes that uniquely identifies a record in a property group. There can be only one primary key in a table and cannot be repeated or null. Primary keys often form referential integrity constraints with foreign keys to prevent data inconsistencies. A unique index is automatically generated for the primary key in the database management system, so the primary key is a special index.

Example:

Student form (student number, name, class)

Since each student's student number is unique, the student number is a primary key.

Course schedule (course ID, course name)

Because the course ID is unique, it is a primary key

Transcript (student number, course ID, grade)

A single attribute in the score sheet can not identify a record, and it needs to be combined with the course ID to identify the record, so the combination of the two is a primary key.

Foreign keys in the database

Foreign keys are used to establish an association with another table and to determine the fields recorded in another table. A foreign key is the primary key of another table, which can be multiple and repeated, or it can be null. The purpose of foreign keys is to keep the data in the table consistent

Example:

As in the case above, the student number is not the primary key in the grade table, but it is the primary key in the student table, so we can say that the student number in the grade table is the foreign key of the student table.

Indexes in the database

An index is used to quickly find records with a specific value. The purpose is to speed up the access speed for the convenience of retrieval, create according to certain rules, and play the role of sorting.

Differences between primary keys, foreign keys, and indexes

The differences between the three are as follows

The primary key foreign key index definition uniquely identifies a record, no duplicates and null values are the primary keys of another table, repeats and null values are not duplicated, but null values can be used to ensure data integrity, establish connections with other tables, improve access speed, only one primary key can have multiple unique indexes, thank you for your reading! So much for understanding what the primary key, foreign key and index are in the database. I hope the above content can be helpful to you so that you can learn more knowledge. If you think the article is good, you can share it and let more people see it.

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