来自函数的 SQL Server 默认列值

Question

I want to set default value to Id column in Person table with a function that goes like this:

Function:

IF OBJECT_ID ( 'GetLastId','FN') IS NOT NULL   
    DROP function GetLastId;  
GO  

CREATE FUNCTION [dbo].[GetLastId]
    (@TableName nvarchar(max)) 
RETURNS int
AS
BEGIN
    DECLARE @LastId int;
    DECLARE @sql nvarchar(max);

    SET @sql = 'SELECT @LastId = ISNULL(MAX(Id), 0) + 1 FROM ' + @TableName + ';'

    EXECUTE sp_executesql @sql, N'@LastId int output', @LastId = @LastId output;

    RETURN @LastId
END

and then:

UPDATE Person 
SET Id = dbo.GetLastId('Person')

Running this code throws an error:

Only functions and some extended stored procedures can be executed from within a function.

So how to fix this and make it work as a default value?

And please do not say "Use triggers..." as I intend to use it with Entity Framework Core as default value for primary keys.

Thanks

Answer 1

You want a stored procedure, not a function:

create procedure [dbo].[GetLastId] (
    @TableName nvarchar(max),
    @LastId int output
) as
begin
   declare @sql nvarchar(max);

   set @sql = 'select @LastId = ISNULL(MAX(Id), 0) + 1 from ' + @TableName + ';'
   EXECUTE sp_executesql @sql,
                         N'@LastId int output',
                         @LastId=@LastId output;
end;

You should also use quotename() around the table name to prevent unexpected things from happening.

Then you would call this as:

declare @lastId int;

exec dbo.GetLastId('Person', @lastid output); 

update Person
    set Id = @lastId;

Answer 2

You need to create stored procedure instead of function

create procedure [dbo].[GetLastId] (
    @TableName nvarchar(max),
    @ColumnName nvarchar(200),
    @LastId int output
) as
begin
   declare @sql nvarchar(max);

   set @sql = 'select @LastId = ISNULL(MAX('+ @ColumnName +'), 0) + 1 from ' + @TableName + ';'
   EXECUTE sp_executesql @sql,
                         N'@LastId int output',
                         @LastId=@LastId output;
end;

Then you can execute sp like below

declare @lastId int

exec dbo.GetLastId 'Person', 'Id' , @lastid output;
select @lastId

update Person
set Id = @lastId;