How to specify annotations for columns when adding a column in SQL

The way to comment a new column in SQL is to use the ALTER TABLE statement, which specifies the comment text after the COMMENT keyword is specified in the ADD COLUMN clause, for example, ALTER TABLE users ADD COLUMN age INTEGER COMMENT 'Age of the user in years', and comments help enhance code readability, force data integrity, and simplify database maintenance.

Add comments to new columns in SQL

Question: How do I specify annotations for newly added columns in SQL?

answer:

The method to add comments to a new column in SQL is as follows:

step:

1. Use the ALTER TABLE statement:

    <code class="sql">ALTER TABLE table_name ADD COLUMN new_column_name data_type COMMENT 'comment text';</code>

2. Specify column comments:

   In the ADD COLUMN clause, specify the column comment after the COMMENT keyword. Comments can be enclosed in single or double quotes.

3. Example:

   To add a comment to a new column age in a table named users , you can use the following statement:

    <code class="sql">ALTER TABLE users ADD COLUMN age INTEGER COMMENT 'Age of the user in years';</code>

4. Verification Note:

   You can use DESC or DESCRIBE statements to verify that the column annotation has been successfully added:

    <code class="sql">DESC table_name;</code>

advantage:

Adding comments to columns has the following advantages:

• Enhanced code readability: Comments provide additional information about the purpose and meaning of columns, making the code easier to understand.
• Forced data integrity: Comments can remind users to use valid values ​​when filling in columns.
• Simplify database maintenance: Annotations help identify and understand changes in data structures.

Notes:

• Not all database systems support column annotations.
• There are limitations on the length of column comments, and the specific values ​​vary by database system.
• Comments do not apply to temporary tables.

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