How to use describe in mysql

The DESCRIBE command in MySQL is used to obtain the metadata information of the table, including: field name, data type, length, whether to allow null values, default value, and key. It returns a result set containing details about the table structure, column types, constraints, and indexes.

DESCRIBE Command in MySQL

DESCRIBE command is used to get metadata information about the tables in the database, e.g. Table structure, column types, constraints and indexes.

Syntax

<code>DESCRIBE <表名>;</code>

Usage

When the DESCRIBE command is executed, it returns a result set containing information about the specified table The following information:

• Field names: The name of each column of the table.
• Data type: The type of data stored in each column, such as INT, VARCHAR, or DATE.
• Length: The maximum number of characters or numeric length allowed per column.
• Whether to allow NULL values: Whether each column is allowed to store NULL values.
• Default value: When inserting a new row, if the column value is not specified, the default value is used.
• Key: Whether the column is part of the primary key, foreign key, or index.
• Additional information: Additional information about the column, such as auto-increment or unique constraints.

Example

Let us use the DESCRIBE command to get metadata information about a table named "customers":

<code>DESCRIBE customers;</code>

Output results Similar to:

<code>Field | Type        | Null | Key | Default | Extra
-------+-------------+------+-----+---------+------
id     | int(11)      | NO   | PRI | NULL     | auto_increment
name   | varchar(255) | NO   |     | NULL     |
email  | varchar(255) | NO   |     | NULL     |</code>

This output means:

• The "customers" table contains four fields: id, name, email and created_at.
• The "id" field is the primary key and allows auto-increment.
• The "name" and "email" fields are of type VARCHAR, allowing storage of up to 255 characters.
• All fields are not allowed to have null values.

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