单排表？ [英] Single Row Table?

问题描述

我有一张桌子应该只包含一行。确实

没有定义任何主键。

所以，基本上，当在该表中发生新的插入时，我想

它如果

表中已经存在一行，则（插入）失败。

我该怎么做？我可以添加任何约束吗？或者我需要写一个

单独的触发器吗？


谢谢和问候，


Yateen V. Joshi

Hi,

I have got a table which is supposed to contain only one row. It does
not have any primary keys defined.
So, essentially, when a new insert happens in that table, I would like
it (the insert) to fail if there is already a row existing in that
table.
How can I do that? Can I add any constraints? Or do I need to write a
separate trigger for the same?

Thanks and regards,

Yateen V. Joshi

推荐答案

2004年8月27日星期五13:32:07 + 0530， />
Yateen Joshi< yj **** @ starentnetworks.com>写道：

On Fri, Aug 27, 2004 at 13:32:07 +0530,
Yateen Joshi <yj****@starentnetworks.com> wrote:

我有一个表应该只包含一行。它确实没有定义任何主键。
所以，基本上，当在该表中发生新插入时，如果已经有一行，我希望它（插入）失败存在于
表中。
我该怎么做？我可以添加任何约束吗？或者我是否需要为它编写单独的触发器？

Hi,

I have got a table which is supposed to contain only one row. It does
not have any primary keys defined.
So, essentially, when a new insert happens in that table, I would like
it (the insert) to fail if there is already a row existing in that
table.
How can I do that? Can I add any constraints? Or do I need to write a
separate trigger for the same?

强制执行此操作的一种简单方法是添加主键和约束

强制主键成为特定值。


--------------------- ------（播出结束）---------------------------

提示2：你可以使用取消注册命令一次性取消所有列表

（发送取消注册YourEmailAddressHere到 ma * ******@postgresql.org ）

A simple way to force this is to add a primary key and a constraint
that forces the primary key to be a particular value.

---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to ma*******@postgresql.org)

On Sun，2004-08-29 15:30，Bruno Wolff III写道：

On Sun, 2004-08-29 at 15:30, Bruno Wolff III wrote:

周五，2004年8月27日13:32:07 +0530，
Yateen Joshi< yj **** @ starentnetworks.com>写道：

On Fri, Aug 27, 2004 at 13:32:07 +0530,
Yateen Joshi <yj****@starentnetworks.com> wrote:

我有一个表应该只包含一行。它确实没有定义任何主键。
所以，基本上，当在该表中发生新插入时，如果已经有一行，我希望它（插入）失败存在于
表中。
我该怎么做？我可以添加任何约束吗？或者我是否需要为它编写一个单独的触发器？

Hi,

I have got a table which is supposed to contain only one row. It does
not have any primary keys defined.
So, essentially, when a new insert happens in that table, I would like
it (the insert) to fail if there is already a row existing in that
table.
How can I do that? Can I add any constraints? Or do I need to write a
separate trigger for the same?

强制执行此操作的一种简单方法是添加主键和约束
主键是一个特定的值。

A simple way to force this is to add a primary key and a constraint
that forces the primary key to be a particular value.

是否合理/可能添加一个检查约束，例如

select count（*）来自表< = 1？

---------------------------（广播结束）--- ------------------------

提示9：如果您的
加入列的数据类型不匹配

Is it reasonable / possible to add a check constraint something like
select count(*) from table <=1?
---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
joining column''s datatypes do not match

On Sun，2004年8月29日15:38:45 -0600，

Scott Marlowe< sm ****** @ qwest.net>写道：

On Sun, Aug 29, 2004 at 15:38:45 -0600,
Scott Marlowe <sm******@qwest.net> wrote:

On Sun，2004-08-29 15:30，Bruno Wolff III写道：

On Sun, 2004-08-29 at 15:30, Bruno Wolff III wrote:

周五，2004年8月27日13:32:07 + 0530，
Yateen Joshi< yj **** @ starentnetworks.com>写道：

On Fri, Aug 27, 2004 at 13:32:07 +0530,
Yateen Joshi <yj****@starentnetworks.com> wrote:

我有一个表应该只包含一行。它确实没有定义任何主键。
所以，基本上，当在该表中发生新插入时，如果已经有一行，我希望它（插入）失败存在于
表中。
我该怎么做？我可以添加任何约束吗？或者我是否需要为它编写一个单独的触发器？

Hi,

I have got a table which is supposed to contain only one row. It does
not have any primary keys defined.
So, essentially, when a new insert happens in that table, I would like
it (the insert) to fail if there is already a row existing in that
table.
How can I do that? Can I add any constraints? Or do I need to write a
separate trigger for the same?

强制执行此操作的一种简单方法是添加主键和约束
主键是一个特定的值。

A simple way to force this is to add a primary key and a constraint
that forces the primary key to be a particular value.

是否合理/可能添加一个检查约束，例如
select table（*）from table< = 1？

Is it reasonable / possible to add a check constraint something like
select count(*) from table <=1?

应该可以使用after触发器来实现，但是有一点

设置更多的工作。只要桌子被吸尘，无论哪种方式

可能都相当快。


--------------- ------------（广播结束）---------------------------

提示2：您可以使用取消注册命令一次性取消所有列表

（发送取消注册YourEmailAddressHere到 ma ******* @ postgresql.org ）

It should be possible to do that with an after trigger, but it is a bit
more work to set up. As long as the table gets vacuumed, either way
is probably reasonably fast.

---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to ma*******@postgresql.org)

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