SQL Server查询需要3分40秒。 如何提高执行时间？

Question

I have a query that is taking 3 min 40 sec.

Here except the AirESet and ELT_B tables, all other tables are lookup tables and there is a lot less data in these tables. Interestingly without these lookup tables execution time was around 30 sec. My understanding is with lookup tables containing a lot less data, performance should not degrade.

SELECT DISTINCT 
    RPGM.GroupID as RegionPerilGroupID,
    RPGM.GroupName as RPGroupName,
    LLGM.GroupID as LossLevelGroupID,
    LLG.GroupName As LLGroupName
FROM
    Acc.dbo.AIRESet ES 
JOIN 
    Acc.dbo.vw_RegionPerilGroup RPGM ON ES.RegionperilID = RPGM.RegionperilID 
                                     AND ModelLossFileID = 65 -- Line of Business
JOIN 
    AR.LA.ELT_B ELT WITH (NOLOCK) ON ES.EventNum = ELT.EventNum 
                                  AND ELT.Versionid = 215 
JOIN 
    AR.LA.LossLevelGroupMappings LLGM ON ELT.LossLevelID = LLGM. LossLevelID 
JOIN 
    AR.LA.LossLevelGroup LLG ON LLGM.GroupID = LLG.GroupID 
                             AND LLG.LosstypeId = 3 
JOIN 
    AR.LA.ReportMap RM ON RPGM.GroupId = RM.RegionPerilGroupID 
                       AND LLGM.GroupID = RM.LossLevelGroupID
JOIN 
    AR.LA.ReportMapFilterMappings RMFM ON RM.ReportMapID = RMFM.ReportMapID
                                       AND RMFM.FilterID = 15
ORDER BY 
    LossLevelGroupID, RegionPerilGroupID 

Answer 1

Let me take a guess.
Please add option (HASH JOIN) to your query.

---

Ps
SELECT distinct ... is usually an indication for query logic issues.
Please find the cause for the duplications.

---

... and -

1. No.
   You don't need indexes for equality join operations.
   This is SQL Server, not MySQL and it supports HASH JOIN.

   Furthermore -
   The use of indexes for retrieval of large data volumes leads to significant degradation in performance.

---

2. No.
   GROUP BY / DISTINCT does not necessarily imply a SORT operation.
   It can be also implemented using HASH with complexity of O(1) instead of O(n*log n).

---

The limitations of statistics

select @@version

---

 Microsoft SQL Server 2014 - 12.0.4213.0 (X64) Jun 9 2015 12:06:16 Copyright (c) Microsoft Corporation Express Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1) 

---

create table t (n int primary key)

;with   t (n) as (select 1 union all select n+1 from t where n < 1000)
insert into dbo.t select n from t option  (maxrecursion 0)

create statistics t_n on t (n)
update statistics t (t_n)

---

;with x as (select * from t where sqrt(n) = n)
select * from x x0,x x1,x x2,x x3,x x4,x x5

---

 +---+---+---+---+---+---+ | n | n | n | n | n | n | +---+---+---+---+---+---+ | 1 | 1 | 1 | 1 | 1 | 1 | +---+---+---+---+---+---+ 

---

HASH JOIN Vs. LOOP JOIN

create table t (i int,j1 int,j2 int,j3 int,j4 int,j5 int)

;with   t (n) as (select 0 union all select n+1 from t where n < 999)
insert into dbo.t (i,j1,j2,j3,j4,j5) 
select      1+t0.n+1000*t1.n,1+t0.n,1+t0.n,1+t0.n,1+t0.n,1+t0.n
from        t t0,t t1 
option      (maxrecursion 0)

create table d1 (j int primary key,k int)
create table d2 (j int primary key,k int)
create table d3 (j int primary key,k int)
create table d4 (j int primary key,k int)
create table d5 (j int primary key,k int)

;with   t (n) as (select 0 union all select n+1 from t where n < 999)
insert into dbo.d1 (j,k) 
select      1+t0.n,1
from        t t0 
option      (maxrecursion 0)

insert into d2 select * from d1
insert into d3 select * from d1
insert into d4 select * from d1
insert into d5 select * from d1

---

select  sum (d1.k+d2.k+d3.k+d4.k+d5.k)

from            t 
        join    d1 on t.j1 = d1.j 
        join    d2 on t.j2 = d2.j 
        join    d3 on t.j3 = d3.j 
        join    d4 on t.j4 = d4.j 
        join    d5 on t.j5 = d5.j 

option (hash join)

---

select  sum (d1.k+d2.k+d3.k+d4.k+d5.k)

from            t 
        join    d1 on t.j1 = d1.j 
        join    d2 on t.j2 = d2.j 
        join    d3 on t.j3 = d3.j 
        join    d4 on t.j4 = d4.j 
        join    d5 on t.j5 = d5.j 

option (loop join)

HASH GROUP Vs. ORDER GROUP

create table t (i int,j int)

;with   t (n) as (select 0 union all select n+1 from t where n < 9)
insert into dbo.t (i,j) 
select      t0.n,t0.n
from        t t0,t t1,t t2,t t3,t t4,t t5,t t6

---

select      distinct
            i,j
from        t
option      (HASH GROUP)
;

select      i,j
from        t
group by    i,j
option      (HASH GROUP)
;

---

select      distinct
            i,j
from        t
option      (ORDER GROUP)
;

select      i,j
from        t
group by    i,j
option      (ORDER GROUP)
;