Please help me with PL/SQL problem

Question

Hi to all
This is my problem. I have a database with several tables. I will mention just some important for this problem. I have a table called Invoice, where I have following atributes
sifrac number(9) not null primary key,
datrac date default sysdate,
sifkup number(5),
sifprod number(5) not null,
ukcena number(5,2)
Then I have table called History of customer where I have
constraint pk_istkup primary key(sifrac,sifkup),
sifrac number(9) constraint fk_sifrac2 references racun(sifrac),
sifkup number(5) constraint fk_sifkup3 references kupac(sifkup) this is primary key in a table customer,
datrac date default sysdate,
ukcena number(5,2) this is total price of purchased stuff per one invoice.
What I would like to do now is make a trigger before insert or update table Invoice which check table History of customer and make a calculation of all total prices per one customer and if that customer made a purchase which is more than 1000 dollars then it have to make a calculation of total price*discount percent.How can I do that.
Thanks to all in advance

Answer 1

Billy  Verreynne  wrote:
LKBrwn_DBA wrote:
This type of functionality (a business rule to compute discount) would normally be added at the application level and not in a trigger. Why? Does business rule code need Java to be expressed correctly? Does Java (or whatever application layer language) used provide a better set of instructions for doing business rules than PL/SQL? Is business code written using a special keyboard and a pretty font?
And what happens when new system feeds invoice data for new department/division directly into the database, bypassing the app layer? What happens to that app layer business logic now?
It is a fallacy that business rules and logic needs to reside in a separate layer as that is somehow better. I disagree. LKBrwn_DBA didn't mention Java as an application layer. And he was not strict about it. So yes it is possible to use a trigger. But business logic tends to be changed fequently. So the rules for the logic might change. I would implement such logic using a pacakged pl/sql api. Triggers I would use for data validations and checks that are less likely to be changed.
As always it depends. But the general advice to have a certain level of business logic (e.g. apis) and another level of data integration and consitency layer (e.g. constraints and triggers) is a good advice.
As for bypassing the application layer. If an new system is able to do that, it can wreck even more havoc. A good anti mechanism is to expose only the APIs layer in a separate schema. The new system will have access to the schema and to the packages that are specified there. But it won't have direct dml to the tables.
Main question for me would be: Is that a business rule or is it a data integration rule (e.g. keep redundant data in different tables harmonized). This influences where the logic will be implemented.
Edited by: Sven W. on Oct 2, 2009 8:59 AM