The methods for creating databases and tables are as follows: 1. Use CREATE DATABASE database_name; Create a database, such as CREATE DATABASE school; 2. You can use IF NOT EXISTS to avoid repeated creation, such as CREATE DATABASE IF NOT EXISTS school; 3. You can specify a character set, such as CREATE DATABASE school CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci; 4. Use USE school; Switch to the target database; 5. Use CREATE TABLE to create tables, such as CREATE TABLE students (id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(100) NOT NULL, age INT, gender ENUM('male', 'female', 'other')); 6. Notes include avoiding duplication of names, avoiding keyword naming, selecting appropriate field types, unified character sets, etc.
Creating databases and tables is a basic operation using MySQL. You may feel a little unfamiliar at first, but in fact, you can get started quickly by mastering a few key commands. Below I will take you step by step to understand how to create databases and data tables in MySQL.
Basic methods to create a database
Before you start building a table, you need to have a database first. The statements to create a database in MySQL are very simple:
CREATE DATABASE database_name;
For example, if you want to create a database called school , you can write it like this:
CREATE DATABASE school;
After the creation is completed, you can use the following command to view all databases and confirm whether they are successful:
SHOW DATABASES;
Sometimes you may encounter problems that already exist in the database. At this time, you can add judgment conditions to avoid errors:
CREATE DATABASE IF NOT EXISTS school;
If you want to specify a character set (such as the commonly used utf8mb4), you can also set it at creation time:
CREATE DATABASE school CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
The advantage of this is that it supports more characters (such as emojis) and is also more suitable for multiple locales.
Use database and create data tables
After creating the database, the next step is to "enter" the database to create tables inside. Use the following command to switch the database:
USE school;
Next is to build a table. The basic syntax is as follows:
CREATE TABLE table_name (
column1 datatype constraints,
column2 datatype constraints,
...
); For example, we want to create a student table students , including student number, name, age, and gender fields:
CREATE TABLE students (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(100) NOT NULL,
age INT,
gender ENUM('male', 'female', 'other')
);Explain these fields:
-
idis the primary key and is automatically incremented, and does not need to be filled in manually every time a new record is inserted; -
nameis a string type, with a length limit of 100 and cannot be empty; -
ageis an integer type; -
genderis an enum type, and can only be male, female, or other.
After executing, you can use this command to see if it is built:
DESCRIBE students;
Common Errors and Precautions
When newbies create databases and tables, they often encounter some common problems. Here are a few things to pay attention to:
- Duplicate database or table name : It is recommended to use
IF NOT EXISTSto avoid error reporting; - Misuse of keywords : For example,
ORDERandGROUPare MySQL keywords, try not to use them to name tables or fields; - Inappropriate field type selection : For example, if the phone number starts with 0, it will cause problems with the INT type, and you should use CHAR or VARCHAR;
- Forgot to use a semicolon : every SQL statement should have a semicolon at the end;
- Character sets are not unified : the character sets of databases, tables and fields are best kept consistent, and it is recommended to use utf8mb4;
In addition, you can also add default values, unique constraints, etc. when creating tables, such as:
email VARCHAR(100) DEFAULT 'no_email@example.com' UNIQUE
Basically that's it. Take your time when you first come into contact with it, start with simple examples, and it is not too late to add complex functions after getting familiar with it.
The above is the detailed content of mysql tutorial for creating a database and table. For more information, please follow other related articles on the PHP Chinese website!
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