postgresql - postgreSQL：如何复制一行

Question

这是我的表 web_book 的方案：

     Column     |          Type          |                       Modifiers                       
----------------+------------------------+-------------------------------------------------------
 id             | integer                | not null default nextval('web_book_id_seq'::regclass)
 page_count     | integer                | not null
 year_published | integer                | not null
 file           | character varying(100) | not null
 image          | character varying(100) | not null
 display_on_hp  | boolean                | not null
 name           | character varying(128) | not null
 description    | text                   | not null
 name_cs        | character varying(128) | 
 name_en        | character varying(128) | 
 description_cs | text                   | 
 description_en | text                   |

该表包含一行，其中id=3. 我想复制该行，但如果我尝试这个：

INSERT INTO web_book SELECT * FROM web_book WHERE id=3;

我明白了：

ERROR:  duplicate key value violates unique constraint "web_book_pkey"
DETAIL:  Key (id)=(3) already exists

Answer 1

您需要为新插入的行创建一个新 ID：

INSERT INTO web_book( 
   id, page_count, year_published, file, image, 
   display_on_hp, name, description, name_cs, 
   name_en, description_cs, description_en
)
SELECT nextval('web_book_id_seq'), 
       page_count, 
       year_published, 
       file, 
       image, 
       display_on_hp, 
       name, 
       description, 
       name_cs, 
       name_en, 
       description_cs, 
       description_en 
FROM web_book WHERE id=3;

正如 ClodoaldoNeto 所提到的，您可以通过简单地省略 ID 列并让默认定义完成其工作来使事情变得更容易：

INSERT INTO web_book( 
   page_count, year_published, file, image, 
   display_on_hp, name, description, name_cs, 
   name_en, description_cs, description_en
)
SELECT page_count, 
       year_published, 
       file, 
       image, 
       display_on_hp, 
       name, 
       description, 
       name_cs, 
       name_en, 
       description_cs, 
       description_en 
FROM web_book WHERE id=3;

在这种情况下，您不需要知道序列名称（但发生的事情不太明显）。

Answer 2

仅当您指定其值时才指定id列（这不是您的情况）。您想使用下一个序列web_book_id_seq值，因此不要在 INSERT 查询中指定它。

您的 INSERT 应如下所示：

INSERT INTO web_book (page_count, year_published, file, image, display_on_hp, name, description, name_cs, name_en, description_cs, description_en)
SELECT page_count, year_published, file, image, display_on_hp, name, description, name_cs, name_en, description_cs, description_en
FROM web_book
WHERE id = 3;