sql - Basic counting queries -


i have 2 tables class , grade.

this sample rows in class table:

c_name....c_time...f_name..c_room...semester inss300...m5:30....dwight..219bc....fall11 inss300...t5:30....keen....216bc....fall11 mkt300....m5:30....lee.....112bc....sp11 mkt300....w5:30....lee.....112bc....sp11 inss421...t5:30....cory....212bc....fall11 fin300....th5:30...keen....219bc....fall11 inss300...w5:30....cory....219bc....fall11 inss300...f5:30....cory....216bc....fall11 inss422...f5:30....keen....219bc....fall11

and sample data in grade table

s_name   c_name     g larry....inss300....b larry....fin300.....a sony.....inss300....c sony.....inss421....c gray.....inss300....c gray.....inss421....d trudy....inss300....b drum.....inss421....a drum.....fin300.....b puri.....inss422....c apple....inss422....c larry....inss422....c larry....inss300....b sony.....inss300....c gray.....inss300....c trudy....inss300....b

my question have answer is:

assume these tables in account ordb002. need give read permission on 3 tables group member sally account ordb009. assuming have given sally read permission on tables. sally wants count of grades (i.e., a, b, c etc..) faculty , course. write query sally count.

i have come query

select cla.f_name      , gra.c_name      , count(grade)      , grade class1 cla     , grade1 gra cla.c_name=gra.c_name group cla.f_name        , gra.c_name        , grade order cla.f_name        , gra.c_name;

which gives me following output:

f_name               c_name     count(grade) g -------------------- ---------- ------------ - cory                 inss300               4 b cory                 inss300               4 c cory                 inss421               1 cory                 inss421               1 c cory                 inss421               1 d dwight               inss300               2 b dwight               inss300               2 c keen                 fin300                1 keen                 fin300                1 b keen                 inss300               2 b keen                 inss300               2 c keen                 inss422               3 c

i don't know why 4b , 4 c coming @ top of output when possibility can 2b , 2 c.

any suggestions?

it's because in class table have "duplicate" rows c_name , f_name, e.g.:

c_name    c_time   f_name  c_room  semester --------- -------- ------- ------- --------   inss300   w5:30    cory    219bc   fall11 inss300   f5:30    cory    216bc   fall11

each row in grade table inss300 going match against rows, resulting in double count.

so, if grade table doesn't note time class was, you're going have filter class table display 1 row per c_name , f_name.

alternatively, group rows in grade table first, , join them class table, if still needed display both rows (although don't think right approach problem you're trying solve).


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