How to use desc in mysql

DESC command is used to obtain the metadata information of the table, including field name, data type, whether it is empty, default value, primary key and foreign key, etc. It returns a table containing Field, Type, Null, Key, Default, Extra and other columns, displaying the field information and constraints of the table.

DESC command in MySQL

The DESC command is an important tool in the MySQL database for obtaining field information in the table. tool. The syntax format is:

<code class="SQL">DESC <表名>;</code>

Usage

The DESC command obtains the metadata information of the specified table, including field name, data type, whether it is empty, default value, and primary key and foreign keys etc. The return result is a table containing the following columns:

• Field: Field name
• Type: Data type
• Null: Whether to allow null
• Key: Primary key or foreign key constraint
• Default: Default value
• Extra: Other information

Detailed explanation

• Field: This column displays the name of the field.
• Type: This column displays the data type of the field. For example, INT, VARCHAR, DATE, etc.
• Null: This column indicates whether the field is allowed to be empty. YES means that it is allowed to be empty, NO means that it is not allowed to be empty.
• Key: This column shows whether the field is a primary key or a foreign key. PRI stands for primary key, MUL stands for index, and FK stands for foreign key.
• Default: This column displays the default value of the field.
• Extra: This column displays additional information such as AUTO_INCREMENT (auto-increment) or TIMESTAMP (timestamp).

Example

The following example queries the field information of the table named "employees":

<code class="SQL">DESC employees;</code>

The results may be as follows:

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

Conclusion

The DESC command is an important tool for obtaining field information in a table and can be used to understand the structure and constraints of the table. It is very useful in database design, debugging and optimization.

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