The following is the set up and test scripts. The test script suppose to scan table T4 only. However, it starts to scan both tables T1 and T4 when they have more than 10000 rows.
create table T1 (A varchar(5) check ((A='S4' or A='S3' or A='S2' or A='S1' or A='FS' or A='FM' or A='FBL' or A='ES' or A='EBL' or A='BL'))
,DateX date
,id char(6)
,DateY date
,primary key clustered (A, DateX, id))
create table T4 (A varchar(5) check ((A='S1780' OR A='C1780' OR A='B1780'))
,DateX date
,id char(6)
,DateY date
,primary key clustered (A, DateX, id));
-- Insert some values
go
create view dbo.tall
as
select * from dbo.T1
union all
select * from dbo.T4
Test code:
declare @A table (A varchar(5) primary key (A));
insert @A
values ('S1780'), ('C1780'), ('B1780');
with a as (select *
from tall
where A in (select *
from @A)
),
sd
as (select A, max(DateY) DateY
from a
group by A
),
filter24m
-- Un-comment the lines in this CTE will make the scanning T1 occur with even less row count
as (select id, a.A --, sd.DateY
from a
join sd on a.A = sd.A
--where DateX between dateadd(mm, 1, sd.DateY) and dateadd(mm, 24 + 1, sd.DateY) --
--group by id, a.A, sd.DateY
--having count(*) = 24
)
--
select *
from filter24m
Bad execution (test when T1 has 100 rows and T4 has 10000 rows):
Table 'T4'. Scan count 2, logical reads 80, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#1B3A42B1'. Scan count 1, logical reads 6, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'T1'. Scan count 3, logical reads 6, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
|--Concatenation
|--Nested Loops(Inner Join, OUTER REFERENCES:([workdb].[dbo].[T1].[A]))
| |--Nested Loops(Inner Join, OUTER REFERENCES:([A]))
| | |--Clustered Index Seek(OBJECT:(@A), SEEK:([A] >= 'B1780' AND [A] <= 'S4') ORDERED FORWARD)
| | |--Stream Aggregate(DEFINE:([workdb].[dbo].[T1].[A]=ANY([workdb].[dbo].[T1].[A])))
| | |--Nested Loops(Inner Join, OUTER REFERENCES:([workdb].[dbo].[T1].[A]))
| | |--Stream Aggregate(DEFINE:([workdb].[dbo].[T1].[A]=ANY([workdb].[dbo].[T1].[A])))
| | | |--Clustered Index Seek(OBJECT:([workdb].[dbo].[T1].[PK__T1__EE1DD21123AC6823]), SEEK:([workdb].[dbo].[T1].[A]=[A]) ORDERED FORWARD)
| | |--Clustered Index Seek(OBJECT:(@A), SEEK:([A]=[workdb].[dbo].[T1].[A]), WHERE:([A]>='B1780' AND [A]<='S4') ORDERED FORWARD)
| |--Clustered Index Seek(OBJECT:([workdb].[dbo].[T1].[PK__T1__EE1DD21123AC6823]), SEEK:([workdb].[dbo].[T1].[A]=[workdb].[dbo].[T1].[A]) ORDERED FORWARD)
|--Merge Join(Inner Join, MERGE:([workdb].[dbo].[T4].[A])=([workdb].[dbo].[T4].[A]), RESIDUAL:([workdb].[dbo].[T4].[A]=[workdb].[dbo].[T4].[A]))
|--Nested Loops(Inner Join, OUTER REFERENCES:([workdb].[dbo].[T4].[A]))
| |--Nested Loops(Inner Join, OUTER REFERENCES:([workdb].[dbo].[T4].[A]))
| | |--Stream Aggregate(GROUP BY:([workdb].[dbo].[T4].[A]))
| | | |--Clustered Index Scan(OBJECT:([workdb].[dbo].[T4].[PK__T4__EE1DD21128711D40]), ORDERED FORWARD)
| | |--Clustered Index Seek(OBJECT:(@A), SEEK:([A]=[workdb].[dbo].[T4].[A]), WHERE:([A]>='B1780' AND [A]<='S4') ORDERED FORWARD)
| |--Clustered Index Seek(OBJECT:(@A), SEEK:([A]=[workdb].[dbo].[T4].[A]), WHERE:([A]>='B1780' AND [A]<='S4') ORDERED FORWARD)
|--Clustered Index Scan(OBJECT:([workdb].[dbo].[T4].[PK__T4__EE1DD21128711D40]), ORDERED FORWARD)
Good (test when both tables have only 100 rows):
Table '#1DE1A532'. Scan count 101, logical reads 202, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'T4'. Scan count 103, logical reads 206, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
|--Nested Loops(Inner Join, OUTER REFERENCES:([Union1006]))
|--Nested Loops(Inner Join, OUTER REFERENCES:([A]))
| |--Clustered Index Seek(OBJECT:(@A), SEEK:([A] >= 'B1780' AND [A] <= 'S4') ORDERED FORWARD)
| |--Concatenation
| |--Filter(WHERE:(STARTUP EXPR([A]='BL' OR [A]='EBL' OR [A]='ES' OR [A]='FBL' OR [A]='FM' OR [A]='FS' OR [A]='S1' OR [A]='S2' OR [A]='S3' OR [A]='S4')))
| | |--Clustered Index Seek(OBJECT:([workdb].[dbo].[T1].[PK__T1__EE1DD21123AC6823]), SEEK:([workdb].[dbo].[T1].[A]=[A]) ORDERED FORWARD)
| |--Filter(WHERE:(STARTUP EXPR([A]='B1780' OR [A]='C1780' OR [A]='S1780')))
| |--Clustered Index Seek(OBJECT:([workdb].[dbo].[T4].[PK__T4__EE1DD21128711D40]), SEEK:([workdb].[dbo].[T4].[A]=[A]) ORDERED FORWARD)
|--Top(TOP EXPRESSION:((1)))
|--Nested Loops(Inner Join, WHERE:([Union1019]=[A]))
|--Concatenation
| |--Filter(WHERE:(STARTUP EXPR([Union1006]='B1780' OR [Union1006]='C1780' OR [Union1006]='S1780')))
| | |--Clustered Index Seek(OBJECT:([workdb].[dbo].[T4].[PK__T4__EE1DD21128711D40]), SEEK:([workdb].[dbo].[T4].[A]=[Union1006]) ORDERED FORWARD)
| |--Filter(WHERE:(STARTUP EXPR([Union1006]='BL' OR [Union1006]='EBL' OR [Union1006]='ES' OR [Union1006]='FBL' OR [Union1006]='FM' OR [Union1006]='FS' OR [Union1006]='S1' OR [Union1006]='S2' OR [Union1006]='S3' OR [Union1006]='S4')))
| |--Clustered Index Seek(OBJECT:([workdb].[dbo].[T1].[PK__T1__EE1DD21123AC6823]), SEEK:([workdb].[dbo].[T1].[A]=[Union1006]) ORDERED FORWARD)
|--Clustered Index Seek(OBJECT:(@A), SEEK:([A] >= 'B1780' AND [A] <= 'S4') ORDERED FORWARD)
Good execution plan in xml:
Bad execution plan in xml: https://docs.google.com/file/d/0B6OXmuJYfpRcU2ZUVFdtLUcxQk83TVFSNUFoZEYtbVdaWU4w/edit?usp=docslist_api
