Big question plz read slowly i need to write a procedure but getting stuck

Question

please read this slowly........
I have two tables content_attributes and RULES
content_attributes with 3 columns and 9 rows as follows
contentname contentattributes value
logo category diagram
logo class image
apple category fruit-----------------------
apple class red-------------------------
apple entitlement diamond-----------------------
computer class electronics
computer category systems
computer subclass chip
computer entitlement machine
RULES has these 3 rows and 6 columns
rule_id rulename category class entitlement subclass
1 r1 diagram image NULL NULL
2 r2 fruit red diamond NULL
3 r3 systems electronics machine chip
I was asked to write a stored procedure...... on top of RULES table .it receives only one input parameter.They said my input parameter will be contentname (i.e it can be apple or logo or computer ) --
NOTE : you can see contentnames in the first table above
let us suppose if i get apple as the input to my procedure
1)Ii should find what all attributes are there for the apple from the content_attributes table
2) i come to know that category , class and entitlement are the attributes and its corresponding attributes it doesnt have subclass as attribute
3) hence my query should be
select * from rules
where category=fruit
and class =red
and entitlement=diamond
and subclass= NULL(since subclass is not present as attribute for apple it should be NULL but some other contentname may have this attribute value and other attributes null ) such as
now lets run the procedure and give another input 'logo'
if i receive input as logo then my query will be
select * from rules
where category= diagram
and class=image
and entitlement=NULL
and subclass = NULL
(entitlement and subclass are null because for the contentname logo these are not present as attributes in the content_attributes table)
basically to explain in one line what i am doing is
see the input.......... find the attributes in content_attributes table......... then use those attributes to query rules table...... the attributes that you dont find put them as NULL.

Answer 1

You could be lazy and decoded your where clauses...
-- All tables where there are 6 rows
select *
from user_tables
where decode(num_rows, 6, 1, 0) = 1;
-- All tables where rownum is null
select *
from user_tables
where decode(num_rows, null, 1, 0) = 1;OR you could could do it the long way and make your where clause more specific...
WHERE (PARAM = COL_VAL OR (PARAM IS NULL and COL_VAL IS NULL))