Question

我创建了2个表，Header和Lines：

CREATE TABLE HEADER 
(
HeaderId int IDENTITY (1,1),
HeaderName varchar(20)
CONSTRAINT pk_header PRIMARY KEY (HeaderId)
);

CREATE TABLE Lines
(
LineId int IDENTITY (1,1),
HeaderId int REFERENCES HEADER(HeaderId),
LineName varchar(20)
CONSTRAINT pk_header_line PRIMARY KEY (LineId, HeaderId)
)

这是插入一些数据后我的Lines表的样子：

LineId  HeaderId    LineName
1       1           Header1 Line1
2       1           Header1 Line2
3       2           Header2 Line1

当HeaderId发生变化时，LineId是否有可能从1开始？

这样的事情：

LineId  HeaderId    LineName
1       1           Header1 Line1
2       1           Header1 Line2
1       2           Header2 Line1

Answer 1

没有内置机制。
您可以在HEADER表中添加lines int列，其中包含每个标题的行数，默认为0.
将记录插入行时，应使用HEADER.lines + 1作为LineId，并将HEADER.lines增加1。
您可以通过应用程序或使用触发器在线上插入来执行此操作在任何情况下都要考虑到Line上的删除会破坏序列。

create table header 
(
    headerid    int         identity (1,1) constraint header_pk_headerid primary key
   ,headername  varchar (20)
   ,lines       int         not null    default (0)
)


create table lines
(
    lineid      int         not null
   ,headerid    int         not null    constraint lines_fk_headerid references header(headerid)
   ,linename    varchar (20)
   ,constraint lines_pk_headerid_lineid primary key (lineid, headerid)
)

go

create trigger lines_trg_ins  
on lines
instead of insert
as  

    declare @lines table (headerid int,lines int)

    update  h
    set     h.lines = h.lines + i.lines
    output  deleted.headerid,deleted.lines into @lines
    from            header as h 
            join    (select headerid,count(*) as lines from inserted group by headerid) as i
            on      i.headerid = h.headerid

    insert into lines (lineid,headerid,linename)
    select  row_number() over (partition by i.headerid order by getdate()) + l.lines,l.headerid,i.linename
    from    inserted i join @lines l on l.headerid = i.headerid

insert into header (headername) values ('header1'),('header2')
insert into lines (headerid,linename) values (1,'header1 line1'),(1,'header1 line2'),(1,'header1 line3'),(2,'header2 line1'),(2,'header2 line2')

select * from header

+----------+------------+-------+
| headerid | headername | lines |
+----------+------------+-------+
| 1        | header1    | 3     |
+----------+------------+-------+
| 2        | header2    | 2     |
+----------+------------+-------+

select * from lines order by headerid,lineid

+--------+----------+---------------+
| lineid | headerid | linename      |
+--------+----------+---------------+
| 1      | 1        | header1 line1 |
+--------+----------+---------------+
| 2      | 1        | header1 line2 |
+--------+----------+---------------+
| 3      | 1        | header1 line3 |
+--------+----------+---------------+
| 1      | 2        | header2 line1 |
+--------+----------+---------------+
| 2      | 2        | header2 line2 |
+--------+----------+---------------+

重置每个外键字段的种子

1 个答案: