sql - 为什么在更改值时查询永远需要

Question

如果我的表 Mission 具有以下结构:

emp_num              int             P.K
from_date            datetime        P.K
to_date              datetime        P.K
mission_location     varchar(200) 
mission_desc         varchar(200)
req_ser              int             P.K
req_year             int             P.K

---

CONSTRAINT [pkc_mission] PRIMARY KEY CLUSTERED 
(
    [emp_num] ASC,
    [from_date] ASC,
    [to_date] ASC,
    [ req_ser] ASC,
    [ req_year] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

---

当我尝试运行此查询时:

select *
from mission where emp_num =5307

它工作得非常快，但是当我尝试使用另一个值运行相同的查询时，它需要很长时间!

select *
from mission where emp_num =4595

Answer 1

请试试这个-

select  *
from    mission with (forceseek)
where   emp_num = 4595