这是我第一次在MS SQL上进行编码，我想确保使用的结构正确。
我正在编写一个插入触发器，它将根据前一个记录的值更新当前记录的几个值。 Cum_cnt字段具有累积计数，它可以在某些点重设，因此如果else语句捕获重设则添加（当值小于前一个值时）。我正在计算记录之间的计数并从以前的记录更新开始时间。
根据我的其他数据库知识，我已经安装了MS SQL数据库并编写了以下触发器。它可以按预期工作，但是我不确定这是否是编写方法，如果我们更新7-8个字段，会不会出现性能问题。
create table t1 (dt datetime, cum_cnt int, cnt int, st_time datetime, ed_time datetime)
--drop trigger t1_Trg
CREATE TRIGGER t1_Trg
ON t1
AFTER INSERT
AS
DECLARE @v_prev_cnt int
DECLARE @v_curr_cnt int
DECLARE @v_prev_dt datetime
DECLARE @v_curr_dt datetime
DECLARE @v_cnt int
BEGIN
select @v_curr_cnt = i.cum_cnt, @v_curr_dt = i.dt from inserted i
select @v_prev_cnt = cum_cnt, @v_prev_dt = dt from t1 where dt = (select max(dt) from t1 where dt < @v_curr_dt)
if (@v_curr_cnt >= @v_prev_cnt)
set @v_cnt = @v_curr_cnt - @v_prev_cnt;
else
set @v_cnt = @v_curr_cnt;
UPDATE t1
SET st_time = @v_prev_dt,
ed_time = @v_curr_dt,
cnt = @v_cnt
FROM t1
where dt = @v_curr_dt
END
--delete from t1
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:01:00.000' ), 10, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:05:00.000' ), 23, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:10:00.000' ), 27, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:13:00.000' ), 32, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:15:00.000' ), 33, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:17:00.000' ), 33, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:19:00.000' ), 41, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:20:00.000' ), 43, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:23:00.000' ), 04, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:26:00.000' ), 08, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:31:00.000' ), 11, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:34:00.000' ), 15, NULL, NULL, NULL);
insert into t1 (dt , cum_cnt , cnt , st_time , ed_time ) values (Convert(datetime, '2019-01-29 13:35:00.000' ), 18, NULL, NULL, NULL);
结果：
select * from t1
dt cum_cnt cnt st_time ed_time
2019-01-29 13:01:00.000 10 10 NULL 2019-01-29 13:01:00.000
2019-01-29 13:05:00.000 23 13 2019-01-29 13:01:00.000 2019-01-29 13:05:00.000
2019-01-29 13:10:00.000 27 4 2019-01-29 13:05:00.000 2019-01-29 13:10:00.000
2019-01-29 13:13:00.000 32 5 2019-01-29 13:10:00.000 2019-01-29 13:13:00.000
2019-01-29 13:15:00.000 33 1 2019-01-29 13:13:00.000 2019-01-29 13:15:00.000
2019-01-29 13:17:00.000 33 0 2019-01-29 13:15:00.000 2019-01-29 13:17:00.000
2019-01-29 13:19:00.000 41 8 2019-01-29 13:17:00.000 2019-01-29 13:19:00.000
2019-01-29 13:20:00.000 43 2 2019-01-29 13:19:00.000 2019-01-29 13:20:00.000
2019-01-29 13:23:00.000 4 4 2019-01-29 13:20:00.000 2019-01-29 13:23:00.000
2019-01-29 13:26:00.000 8 4 2019-01-29 13:23:00.000 2019-01-29 13:26:00.000
2019-01-29 13:31:00.000 11 3 2019-01-29 13:26:00.000 2019-01-29 13:31:00.000
2019-01-29 13:34:00.000 15 4 2019-01-29 13:31:00.000 2019-01-29 13:34:00.000
2019-01-29 13:35:00.000 18 3 2019-01-29 13:34:00.000 2019-01-29 13:35:00.000