Information Technology Reference
In-Depth Information
The syntax for the algorithm Join is:
Relational
Network
Exec SQL Declare C
cursor for
Select F1, F2….Fn
from Table-T1,
Table-T2.
End-exec.
Find first N
i
record within IX
i
.
Find first N
k
record within IX
k
.
If record-found
perform LOOP1 until
end-of-record.
LOOP1.
If f1=v1 and f2=v2
Obtain N
i
record
Obtain N
k
record.
Perform LOOP2 until
end-of-record.
Find next N
i
record within IX
i
.
Exec SQL Open C
end-exec.
Exec SQL Fetch C into
T end-exec
LOOP2.
Find next N
k
record within IX
k
.
If f1=v1 and f2=v2
Obtain N
i
record
Obtain N
k
record.
Relational Operation Insertion
Attribute values are specified for a tuple to be inserted in a relation R
k
. We denote
by v
1
, v
2
…. v
n
the values for attributes corresponding to fields in N
k
and with V
1
, V
2
… V
f
the values of the foreign keys in R
k
.
Algorithm
Insertion
1.
locate
the owner record type N
k-1
of to-be-inserted record N
k
within secondary indices IX
k-1
using ID
k-1.
/* ID
k-1
= record
identifier value in IX
k-1
*/
2.
locate
to-be-inserted record types N
k
within secondary indices
IX
k
using ID
k
./* ID
k
is the record identifier value in IX
k
*/
3.
Establish contents of all N
k
record data items in working
storage (v
1
,v
2….
v
n,
V
1,
V
2…
V
f
).
4.
store
N
k
record
5.
connect
N
k
record to all owners record N
k-1
in manual sets that
have been established its currency in 2.
Search WWH ::
Custom Search