MySql constraints and indexes: how to create a database efficiently

With the development of the information age, data management has become more and more important, and the database is one of the most basic data management tools. Databases perform well in areas that require large amounts of information storage, quick retrieval of information, and ensuring data consistency. In the creation process of a database, the design of its structure and performance is a very critical step. This article will introduce you to how to use MySql constraints and indexes to improve data quality and performance when creating a database.

Constraints of MySql

Constraints of MySql refer to the rules that limit the data in the database, ensuring that the data meets the specified requirements when inserting or updating. The constraint types supported by MySql include primary key constraints, unique constraints, foreign key constraints, non-null constraints, default value constraints, etc., which are introduced one by one below:

1. Primary key constraints

Primary key A constraint is a column in a table that uniquely identifies a data record. The value of the primary key column must be unique and cannot be null. Primary key constraints are declared when defining the table, can be declared separately when creating the table, or can be added later using the ALTER TABLE statement. For example:

CREATE TABLE employee (

id INT PRIMARY KEY,
name VARCHAR(50),
age INT

);

The id column in this table is the primary key constraint, which means that the id value of each data record must be unique, and Cannot be null.

2. Unique constraint

The unique constraint requires that the value of the column must be unique, but null values ​​are allowed. A table can have multiple unique constraint columns, which are used similarly to primary key constraints. For example:

CREATE TABLE employee (

id INT,
email VARCHAR(50) UNIQUE,
name VARCHAR(50),
age INT

);

In this table, the email column is the only constraint, which means that the email value must be unique, but can be empty.

3. Foreign key constraints

Foreign key constraints are used to ensure that the data in the table have correct relationships. A foreign key constraint is a list of one or more columns whose values ​​must match the values ​​of a primary key or unique constraint column in another table. For example:

CREATE TABLE employee (

id INT PRIMARY KEY,
name VARCHAR(50),
age INT,
department_id INT,
FOREIGN KEY (department_id) REFERENCES department(id)

);

In this table, the department_id column is defined as a foreign key constraint, and the REFERENCES keyword is used to reference other tables The primary key or unique constraint column.

4. Non-null constraint

The non-null constraint is used to ensure that the value of the column is not NULL. For example:

CREATE TABLE employee (

id INT PRIMARY KEY,
name VARCHAR(50) NOT NULL,
age INT

);

In this table, the name column does not allow null values.

5. Default value constraint

The default value constraint is used to ensure that when new data is inserted, if the value of the column is not specified, the default value is used. For example:

CREATE TABLE employee (

id INT PRIMARY KEY,
name VARCHAR(50),
age INT,
hire_date DATE DEFAULT '2020-01-01'

);

In this table, the hire_date column defines a default value of January 1, 2020. If data is inserted If no value is specified for this column, the default value is automatically used.

MySql's index

MySql's index is a data structure created in a table to quickly find and access data in the table. The index types supported by MySql include B-tree index, full-text index, hash index, etc., which are introduced one by one below:

1. B-tree index

B-tree index is The most commonly used index type, which can quickly find data records. B-tree indexes include primary key indexes, unique indexes and ordinary indexes, and they are created in the same way.

Primary key index and unique index are indexes built on a single column or multiple columns. The primary key index is the index on the primary key column in the table. The unique index is the index on the unique value column. They require the index column The value is unique.

Ordinary indexes have no uniqueness requirements and allow duplicate values ​​to appear in index columns. For example:

CREATE TABLE employee (

id INT PRIMARY KEY,
name VARCHAR(50),
age INT,
INDEX name_index (name)

);

In this table, the name_index column is defined as a normal index column to speed up the search for the name column. .

2. Full-text index

Full-text index is an index used to search columns containing text. It can quickly find text data containing keywords. For example:

CREATE TABLE article (

id INT PRIMARY KEY,
title VARCHAR(50),
content TEXT,
FULLTEXT search_index (title, content)

);

In this table, the search_index column is defined as a full-text index column, used to speed up the title and content columns search.

3. Hash index

Hash index is an index based on a hash algorithm, which can quickly locate data records. Hash indexes can only be used for equality queries, not range queries and sorting. For example:

CREATE TABLE student (

id INT PRIMARY KEY,
name VARCHAR(50),
age INT,
INDEX age_index (age) USING HASH

);

In this table, the age_index column is defined as a hash index column, used to speed up the age column Find.

Conclusion

When creating a database, constraints and indexes are very important key factors. Proper use of them can improve the data quality and performance of the database. When using constraints and indexes, you should choose the appropriate type according to the characteristics and needs of the data in order to achieve the best results.

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