What is the usage of comments in MySQL?

In MySQL, the comment feature is used to add additional information to database objects such as tables, columns, indexes, etc. This feature helps developers and other users to understand and use the database more easily.

There are several different ways to use the word “comment.”

1. Add comments when creating a table.

CREATE TABLE table_name (
    column1 datatype COMMENT 'comment',
    column2 datatype
);

When creating a table, you can add the COMMENT keyword after the column definition and provide the comment information within quotation marks.

1. Add comments when modifying table structure.

ALTER TABLE table_name MODIFY column_name datatype COMMENT 'comment';

You can modify columns in a table using the ALTER TABLE statement, and use the COMMENT keyword in the modification statement to add comments.

1. View the comments on the table:

SHOW CREATE TABLE table_name;

You can use the SHOW CREATE TABLE statement to view the complete statement for creating a table, which includes comments for both the table and its columns.

1. View the comments of the column:

SHOW FULL COLUMNS FROM table_name;

The SHOW FULL COLUMNS statement can be used to view detailed information about all columns in a table, including column comments.

1. Add comments when adding an index.

CREATE INDEX index_name ON table_name (column_name) COMMENT 'comment';

When creating an index, you can use the COMMENT keyword to add a comment.

It is important to note that comments are only an auxiliary explanation and do not have any impact on the actual operation of the database. In practical development, using comments properly can enhance the readability and maintainability of the code.