How to create a view consisting of data from tables in2 different databases

Question

Using Oracle 10.2g
I have 2 databases Gus and haggis on Comqdhb schema.
glink indicates a databse link between Haggis and Gus
In Gus there are tables student,subject,grade,school containing columns like upn...
STUDENT
upn
academicYear
SUBJECT
subject
GRADE
examlevel
grade
SCHOOL
sn
In HAGGIS there are tables student,grade,teacher containing columns upn...desc below.
STUDENT
upn
GRADE
grade
upn
academicyear
level
Create view in your HAGGIS database which will join all of the exam grades together. You should have one view which will produce the following relation :
examGrade(upn, subject, examlevel, sn, grade,academicYear)
so I need to create a view which gets the data from both the tables in both the databases.
create view as examGrade(upn, subject, examlevel, sn, grade,academicYear) as select s.upn
But i am not getting how to select a column from 2 tables in different databases
I mean if i said
select upn from comqdhb.student@glink,comqdhb.student;
select upn from comqdhb.student@glink,comqdhb.student
ERROR at line 1:
ORA-00918: column ambiguously defined
help me out,Thank you.

Answer 1

Thank you for the reply will follow up the code format
Create views in your HAGGIS schema database which will join all of the exam grades together. You should have one view which will produce the following relation :
examGrade(upn, subject, examlevel, sn, grade,academicYear)
I understand that there wont be duplication when we use conditions
If i query
select count(upn)
from   comqdhb.student@glink I get 9000
but after the union
create view examGrade(upn, subject, examlevel, sn, grade,academicYear)
as
select distinct s.upn as upn
,                  g.subject as subject
,                  g."LEVEL" as examlevel
,                  g.grade as grades
,                  '9364097'
,                  to_number(g.academicyear) as academicyear
from             comqdhb.student s
,                   comqdhb.grade g
where           s.upn=g.upn
union
select            s.upn
,                   sb.subject
,                   g.elevel
,                   g.grade
,                   s.acyr
,                   sc.sn
from              comqdhb.subject@glink sb
,                   comqdhb.student@glink s
,                    comqdhb.gradevalues@glink g
,                    comqdhb.school@glink sc,
,                    comqdhb.studentingroup@glink sg
,                    comqdhb.teachinggroup@glink tg
where            sb.sid=tg.sid
and                tg.gid=sg.gid
and                sg.upn=s.upn
and                g."LEVEL"=tg.elevel
and                s.school=sc.id
and                sc.id=tg.id; returns
count(upn) from exam gradeIt gets stuck actually sometimes it returns
932002 some results.
2:
Another problem i am having which i am trying to solve and written up my ideas but haven't been getting the expected results.Hope you can help.Thank you.
Information:
=======
All children take exams at the age of 16 called a General Certificate of SecondaryEducation (GCSE).
They have to study and take exams in Mathematics, English and Science, and can take other subjects such as History, French, Art etc. Most students will study between 5 and 10 different subjects before taking their GCSEs.
For each exam, a student is awarded a grade from A*, A, B,C,D,E,F,G,U,X An A* grade is the best grade achievable and an X is the worst grade.
In order to analyze how students have performed, each grade is mapped to a numeric value as follows:
Grade Numerical score
A* 8
A 7
B 6
C 5
D 4
E 3
F 2
G 1
U 0
X 0
Now why i need this avgGCSE is because i have to create a view containing avgGCSE of the students it is used in the next question where a condition is avgGCSE is between 6.5 and 7
In order to calculate the avgGCSE the idea is to calculate the grades of the students and map the grades to their corresponding scores/values
add them all up and div by the total no of grades to get the avg.
desc comqdhb.STUDENT@glink;
STUDENT
=======
UPN
FNAME
CNAME
DOB
GENDER
PREVIOUSSCHOOL
XGCSE
SCHOOL
ACYR
STUDENTINGROUP
=============
UPN
GID
STARTDATE
ENDDATE
GRADE
GRADEVALUES
===========
GRADE
LEVEL
VALUE
I have a opinion that xgcse in STUDENT table refers to the avgGCSE which i want to calculate as when i asked my professor as to what xgcse he said that he forgot to take it out of the table and it is not necessary while creating avggcse.
select *
from comqdhb.student@glink
where xgcse<6.5; Displaying a result
returns:
UPN FAMILYNAME COMMONNAME DATEOFBIR GENDER PREVIOUSSCHOOL XGCSE SCHOOL ACYR
===========================================================================
1011 KIMBERLY ABBOT 07-JUL-79 f none 3.93500948 2 2
select *
from comqdhb.student@glink
where xgcse between 6.5 and 7 and upn = 1386; Displaying a result
returns:
UPN FAMILYNAME COMMONNAME DATEOFBIR GENDER PREVIOUSSCHOOL XGCSE SCHOOL ACYR
===========================================================================
1386 STEPHANIE AANNESSON 15-JAN-79 f none 6.88873 2 2 so if xgcse is the avgGCSE then upn 1011 has avggcse<6.5 and 1386 has avggcse >6.5
my idea was backward strategy like so now if we find out upn 1368 has suppose xgcse(avggcse)>6.5 how to extract the avggcse for the particular upn We need to map grades from GRADEVALUES to grade in STUDENTINGROUP and map upn from studentingroup to upn in student to output the values for the corresponding grades from GRADEVALUES
select grade
from comqdhb.studentingroup@glink
where upn = 1011;
Result:
GRADE
=====
D
F
B
E
C
E
E
B
8 rows selected. Mapping each grade to the corresponding value and calculating we get
32/8=4 total(values to corresponding grades)/no of grades.
But the xgcse for upn 1011 is 3.935 and i am getting 4!! maybe xgcse isn't avggrade but ? is the procedure by me correct for calculating avggcse
select grade
from comqdhb.studentingroup@glink
where upn = 1386;
Result:
GRADE
======
A*
A*
A*
A*
B
A*
A*
A
B
B
B
11 rows selected. grade to the corresponding value and calculating we get
79/11=7.12 total(values to corresponding grades)/no of grades.
But the xgcse for upn 1011 is 6.88... and i am getting 7.12!!
But another problem
when i say
select   g.value,g.grade
from     comqdhb.gradevalues@glink g
,        comqdhb.studentingroup@glink sg
where    g.grade=sg.grade
and      sg.upn=1011;
result:
======
VALUE GRADE
===========
  100 B
  100 B
   80 C
   60 D
   40 E
   40 E
   40 E
   20 F
    6 B
    6 B
    5 C
VALUE GRADE
=============
    4 D
    3 E
    3 E
    3 E
    2 F
16 rows selected.
select   distinct g.value,g.grade
from     comqdhb.gradevalues@glink g
,        comqdhb.studentingroup@glink sg
where    g.grade=sg.grade
and      sg.upn=1011;
result:
======
VALUE GRADE
============
     2 F
   100 B
     6 B
     3 E
    60 D
     5 C
     4 D
    80 C
    40 E
    20 F
10 rows selected. I am getting only 8 for the query
select grade
from comqdhb.studentingroup@glink
where upn = 1386; here its becomming 10 and also its displaying values as 100 and ...
select distinct *
from   comqdhb.gradevalues@glink;
GRADEVALUES
===========
LEVEL      GRADE           VALUE
================================
a          A                 120
a          B                 100
a          C                  80
a          D                  60
a          E                  40
a          F                  20
a          U                   0
a          X                   0
g          A                   7
g          A*                  8
g          B                   6
LEVEL      GRADE           VALUE
================================
g          C                   5
g          D                   4
g          E                   3
g          F                   2
g          G                   1
g          U                   0
g          X                   0
18 rows selected. I was hoping if i could map the grades and get the values and calculate avggrade by total(values)/count(values)that would be it but here there are values like 100...
select  sum(g.value)/count(g.grade) as avggrade
from    comqdhb.gradevalues@glink g
,         comqdhb.studentingroup@glink sg
where  g.grade=sg.grade
and     sg.upn=1386;
avggrade
========
37.4375 the avggrade cant be this big and when i map each grade i obtained for 1368 like a to 7+b to 6 so on i get avggrade 7.12
kindly help.
Edited by: Trooper on Dec 15, 2008 4:49 AM