The key to creating a MySQL table is to master the basic syntax and common options of CREATE TABLE statements. 1. The basic syntax requires specifying field names, data types and constraints, such as NOT NULL, PRIMARY KEY, AUTO_INCREMENT; 2. Common field types include INT, VARCHAR(n), TEXT, DATE, DATETIME, TIMESTAMP and DECIMAL(m,d), and should be selected according to actual needs to optimize storage and performance; 3. The constraints include NOT NULL, UNIQUE, DEFAULT, PRIMARY KEY and FOREIGN KEY. When using foreign keys, the two tables must be engines that support foreign keys (such as InnoDB); 4. CREATE INDEX can be used. Adding indexes improves query efficiency, but avoids excessive use to avoid affecting write performance; 5. Common errors include field name spelling errors, primary key omissions, data type mismatch, engine not specified, and character set inconsistent. It is recommended to use utf8mb4 uniformly and explicitly declare ENGINE=InnoDB and DEFAULT CHARSET=utf8mb4 in the table creation statement.
When creating a MySQL table, the CREATE TABLE statement is one of the most basic and critical operations. Mastering basic syntax structures and common options can help you design your database more efficiently.
Basic syntax structure
The standard syntax for creating tables in MySQL is as follows:
CREATE TABLE table_name (
column1 datatype constraints,
column2 datatype constraints,
...
); Each field (column) must specify the data type, and constraints can also be added, such as NOT NULL , PRIMARY KEY , AUTO_INCREMENT , etc.
For example, create a user table:
CREATE TABLE users (
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(50),
email VARCHAR(100) NOT NULL,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (id)
);The above statement contains common uses such as primary key settings, self-increasing fields, and default values.
Common field types and selection suggestions
MySQL supports a variety of field types, commonly used ones include:
-
INT: integer type, suitable for ID, quantity, etc. -
VARCHAR(n): variable length string, suitable for username, title, etc. -
TEXT/LONGTEXT: Large text content, such as the main text of the article -
DATE/DATETIME/TIMESTAMP: Time-dependent, pay attention to time zone processing differences -
DECIMAL(m,d): exact value, suitable for amount field
Some points to pay attention to when selecting a field type:
- Try to choose the appropriate data type according to actual needs to avoid wasting space or restricting expansion
- Don't set the string length to 255 at will, it is more reasonable to set it as needed.
- For fields that are frequently queried, you must first choose the type before considering index optimization.
Key points for constraints and index settings
In addition to field types, common constraints include:
-
NOT NULL: Not allowed to be empty -
UNIQUE: Unique constraints -
DEFAULT value: Set the default value -
PRIMARY KEY: Primary key, generally used with self-increase -
FOREIGN KEY: Foreign key, used to associate other tables
For example, set foreign keys:
CREATE TABLE orders (
order_id INT PRIMARY KEY AUTO_INCREMENT,
user_id INT,
amount DECIMAL(10,2),
FOREIGN KEY (user_id) REFERENCES users(id)
);It should be noted that foreign keys require both tables to use engines that support foreign keys (such as InnoDB).
In addition, if a certain field is often used as query conditions, you can consider adding an index to improve query efficiency:
CREATE INDEX idx_email ON users(email);
But do not over-index, as it will affect the write performance.
Common Errors and Precautions
Probably encountered problems when writing CREATE TABLE statements include:
- The field name is incorrectly spelled or used reserved words. It is recommended that the field name be enclosed in backticks, such as
`order` - Forgot to add
PRIMARY KEYto the primary key, causing the table to not be used normally - Data type mismatch, such as placing long text in
VARCHAR(50) - The engine is not specified, the default may be MyISAM, and you want to use InnoDB
- There is no unified character set, Chinese garbled code, it is recommended to use
utf8mb4uniformly
You can add these settings at the end of the table creation statement:
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
This can avoid many follow-up problems.
Basically that's it. The grammar is not complicated, but some details are easy to ignore, especially when you are just starting out. Write a few more times and check the document a few times, and you will soon be able to master it.
The above is the detailed content of mysql create table syntax. For more information, please follow other related articles on the PHP Chinese website!
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