Sql 如何向表中添加说明

我知道\d+列出了表格及其说明，例如：

                           List of relations
 Schema |      Name       | Type  |  Owner  |    Size    | Description
--------+-----------------+-------+---------+------------+-------------
 public | table1          | table | me      | 123 kB     |
 public | table2          | table | me      | 123 kB     |
 public | table3          | view  | me      | 123 kB     |
 public | table4          | table | me      | 123 kB     | some description
 public | table5          | table | me      | 123 kB     |
 public | table6          | table | me      | 123 kB     | another description
(6 rows)

我想知道如果一个描述不存在，如何修改或写一个

comment on table table1 is 'This is a new description';
comment on table table4 is 'This is a changed description';

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