# Comment

Adds a comment or removes an existing comment for an existing table or column object.

## COMMENT

```sql
COMMENT ON (TABLE | COLUMN) <object_name> IS (<string_literal> | NULL);
```

Create or remove a comment for a `TABLE` or `COLUMN` object of name `object_name`. The comment must be a string literal or `NULL`. If `NULL`, the comment is removed.\
\
Only super-users or owners of the object can modify comments on the object.

Column and table comments can be viewed either in the `information_schema` system tables, or in the result of the `SHOW CREATE TABLE` command run on the relevant table.

{% hint style="info" %}
Currently comments are not supported with the `CREATE TABLE` command, and `COMMENT ON` is the canonical means to set or unset comments.
{% endhint %}

### **Examples**

1. Create a table and add a comments to it.

{% code overflow="wrap" %}

```sql
CREATE TABLE employees (id INT, salary BIGINT);
-- Add a comment to the 'employees' table
COMMENT ON TABLE employees IS 'This table stores employee information';
-- Add a comment to the 'salary' column
COMMENT ON COLUMN employees.salary IS 'Stores the salary of the employee';
```

{% endcode %}

{% hint style="info" %}
When specifying the name of the `COLUMN` object, it must be of the form `<TABLE>.COLUMN>` to uniquely identify it.
{% endhint %}

2. Show the comments and the DDL of the table.

{% code overflow="wrap" %}

```sql
SHOW CREATE TABLE employees;

CREATE TABLE employees /* This table stores employee information */ (
  id INTEGER,
  salary BIGINT /* Stores the salary of the employee */);
1 rows returned.
```

{% endcode %}

{% hint style="info" %}
Currently `COMMENT ON` is supported only on tables and and columns of that table. Other objects such as `VIEW` are not currently supported.
{% endhint %}

3. View the table and column comment in respective system table.

{% code overflow="wrap" %}

```sql
-- Connect to information_schema database
\c information_schema admin XXXXXXXX

-- Select subset of columns from the tables system table
SELECT table_id,table_name,"comment" FROM tables where table_name = 'employees';

-- Returns one result for the table comment
table_id|table_name|comment
5|employees|This table stores employee information
1 rows returned.

-- Select subset of columns from the columns system table
SELECT table_id,table_name,column_id,column_name,"comment" FROM columns where table_name = 'employees';

-- Returns two results, one of the columns has no comment.
table_id|table_name|column_id|column_name|comment
5|employees|1|id|NULL
5|employees|2|salary|Stores the salary of the employee
2 rows returned.
```

{% endcode %}


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