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Фрагмент инструкции
Manual
Structure
One
of
y
our
tasks
for
this
lesson
requires
that
y
our
rep orts
use
k
ey
ed
Exercise
3:
access
and
that
y
ou
demonstrate
the
p erformance
improv
emen
ts
of
Understanding
k
ey
ed
as
against
serial
access.
The
p erformance
improv
emen
ts
will
Key
ed
Access
only
b e
apparen
t
once
the
rep ort
is
run.
Therefore,
this
comparison,
and
a
detailed
examination
of
access
tuning
and
metho ds,
are
discussed
at
the
end
of
Lesson
4,
when
y
ou
run
the
rep ort.
This
exer
cise
takes
ab
out
15
minutes.
The
rst
part
of
this
exercise
is
a
reading
exercise.
Read
the
follo wing
paragraphs
for
an
understanding
of
k
ey
ed
access
v
ersus
default
access.
By
default,
BR
W
reads
eac
h
source
table
serially
,
in
the
order
Default
Access
sp ecied
on
the
Dene
T
able
screen.
BR
W
reads
eac
h
table
serially
in
to
a
w
orkle.
It
then
sorts
the
w
orkle,
using
the
common
item
dened
in
the
relation
as
the
sort
k
ey
.
F
or
example,
the
Dene
T
able
screen
for
ORDER-PR
ODUCTS
lists
the
tables
in
the
order
PR
ODUCTS,
ORDER-DET
AILS,
and
ORDERS.
BR
W
reads
the
PR
ODUCTS
data
set
in
to
a
w
orkle.
This
le
is
sorted
on
PR
ODUCT-NO.
It
then
reads
the
data
set
ORDER-DET
AILS
in
to
a
second
w
orkle,
and
sorts
it
on
PR
ODUCT-NO.
Then
it
joins
the
t
w
o
w
orkles,
on
PR
ODUCT-NO,
and
writes
the
resulting
records
in
to
a
third
w
orkle.
Y
ou
can,
ho
w
ev
er,
sp ecify
b oth
the
order
in
whic
h
the
data
sets
are
Tuned
Access
read,
and
the
metho d
of
access.
F
or
example,
y
ou
kno
w
that
y
ou
w
an
t
to
read
all
the
records
in
ORDERS,
so
that
y
ou
can
determine
whic
h
orders
w
ere
for
June.
It
is
b etter
to
read
this
data
set
serially
,
b ecause
y
ou
w
an
t
to
read
all
the
records
in
it.
But
note
data
set
ORDER-DET
AILS.
Y
ou
only
w
an
t
to
access
the
items
in
this
data
set
that
match
the
ORDER-NO
in
ORDERS.
So
y
ou
can
use
k
ey
ed
access
to
ORDER-DET
AILS,
on
the
item
ORDER-NO.
That
is,
when
y
ou
ha
v
e
found
the
v
alues
of
ORDER-NO
in
ORDERS
that
apply
to
June,
y
ou
can
use
those
v
alues
as
k
eys
in
to
the
data
set
ORDER-DET
AILS.
In
this
w
a
y
,
y
ou
do
not
ha
v
e
to
read
ORDER-DET
AILS
in
to
a
w
orkle
and
sort
it.
Using
k
ey
ed
access,
y
ou
kno
w
that
y
ou
will
directly
retrieve
the
records
that
y
ou
w
an
t.
The
same
is
true
of
data
set
PR
ODUCTS.
Y
ou
only
w
an
t
information
on
those
pro ducts
that
ha
v
e
b een
ordered
in
June,
that
is,
that
are
presen
t
in
the
table
ORDER-PR
ODUCTS.
So,
if
y
ou
use
k
ey
ed
access
on
PR
ODUCT-NO,
using
the
v
alues
of
PR
ODUCT-NO
found
in
ORDER-DET
AILS,
y
ou
will
automatically
ha
v
e
the
records
that
y
ou
w
an
t
without
an
y
sorting.
So,
b
y
altering
the
sequence
in
whic
h
the
tables
are
accessed,
and
b
y
using
k
ey
ed
access
on
PR
ODUCTS
and
ORDER-DET
AILS,
y
ou
can
improv
e
rep ort
p erformance.
Y
ou
tune
the
rep ort's
p erformance
on
the
T
une
Access
screen.
LESSON
4:
Considering
P
erformance
5-13
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