Trying to understand how the AND and OR keywords works

Question

I read that the precedence of using AND and OR in the where clause can be determined by where you put the parenthesis. I tested it and it is true. How come .........
THIS.....
SELECT invoice_number, invoice_date, invoice_total
FROM invoices
WHERE (invoice_date > '01-MAY-2008' OR invoice_total > 500)
AND invoice_total - payment_total - credit_total > 0
Order By Invoice_Number; AND THIS....
SELECT invoice_number, invoice_date, invoice_total
From Invoices
WHERE invoice_date > '01-MAY-2008' OR invoice_total > 500
And Invoice_Total - Payment_Total - Credit_Total > 0
ORDER BY invoice_number;GIVE ME DIFFERENT RESULTS BUT THIS..............
Select distinct (Select Count(Invoices.Vendor_Id) From Invoices Where Invoices.Invoice_Date < '01-MAY-2008')  as Test_Column
From Invoices
Where (Invoice_Date > '01-MAY-2008' Or Invoice_Total > 500)
And Invoice_Total - Payment_Total - Credit_Total > 0;AND THIS.............
Select distinct (Select Count(Invoices.Vendor_Id) From Invoices Where Invoices.Invoice_Date < '01-MAY-2008')  as Test_Column
From Invoices
Where Invoice_Date > '01-MAY-2008' Or Invoice_Total > 500
And Invoice_Total - Payment_Total - Credit_Total > 0;DONT GIVE ME DIFFERENT RESULTS.
Edited by: mookjais on Feb 24, 2011 8:43 PM

Answer 1

I tested the statements and the syntaxes (sp) are correct, here is the table. It's a sample table so I can give all the values that are in the table also.
CREATE TABLE invoices
  invoice_id            NUMBER,
  vendor_id             NUMBER          NOT NULL,
  invoice_number        VARCHAR2(50)    NOT NULL,
  invoice_date          DATE            NOT NULL,
  invoice_total         NUMBER(9,2)     NOT NULL,
  payment_total         NUMBER(9,2)                 DEFAULT 0,
  credit_total          NUMBER(9,2)                 DEFAULT 0,
  terms_id              NUMBER          NOT NULL,
  invoice_due_date      DATE            NOT NULL,
  payment_date          DATE,
  CONSTRAINT invoices_pk
    PRIMARY KEY (invoice_id),
  CONSTRAINT invoices_fk_vendors
    FOREIGN KEY (vendor_id)
    REFERENCES vendors (vendor_id),
  CONSTRAINT invoices_fk_terms
    FOREIGN KEY (terms_id)
    REFERENCES terms (terms_id)
);Edited by: mookjais on Feb 24, 2011 8:45 PM