将列默认值绑定到 SQL 2005 中的函数 [英] Bind a column default value to a function in SQL 2005

问题描述

我有一列包含可由用户排序的项目:

I have a column containing items that can be sorted by the user:

DOC_ID  DOC_Order DOC_Name
   1       1        aaa
   2       3        bbb
   3       2        ccc

我正在尝试找出一种在创建条目时正确初始化 DOC_Order 的方法.一个好的值要么是相应的 DO-CID(因为它是自动分配的)，要么是 MAX(DOC-ORDER) + 1

I'm trying to figure out a way to properly initialize DOC_Order when the entry is created. A good value would either be the corresponding DO-CID (since it is autoassigned), or MAX(DOC-ORDER) + 1

经过一番谷歌搜索后，我发现可以将标量函数的返回值分配给默认列.

After a bit of googling I saw it was possible to assign a scalar function's return to the default column.

CREATE FUNCTION [dbo].[NEWDOC_Order] 
(
)
RETURNS int
AS
BEGIN

RETURN (SELECT MAX(DOC_ORDER) + 1 FROM DOC_Documents)

END

但我每次使用 MS SQL 管理工作室的尝试都以验证‘DOC_Order’列的默认值时出错"消息告终.

But each of my tries using MS SQL Management studio ended in a "Error validating the default for column 'DOC_Order'" message.

知道将函数分配给 DEFAULT 的确切 SQL 语法是什么吗?

Any idea of what the exact SQL syntax to assign a function to DEFAULT is?

推荐答案

像这样添加默认值的语法是

The syntax to add a default like that would be

alter table DOC_Order 
add constraint 
df_DOC_Order 
default([dbo].[NEWDOC_Order]())
for DOC_Order

另外，当 DOC_Order 为 null 时，您可能希望更改您的函数以进行处理

Also, you might want to alter your function to handle when DOC_Order is null

Create FUNCTION [dbo].[NEWDOC_Order] 
(
)
RETURNS int
AS
BEGIN

RETURN (SELECT ISNULL(MAX(DOC_ORDER),0) + 1 FROM DOC_Documents)

END

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