Assign variable error if 'no rows selected' from query - plsql

Question

I want to assign a variable from the sale of today by the menu item input. If the menu item has been sold yet, the variable should return 0. But it showed error instead:
Error report -
SQL Error: ORA-00905: missing keyword
00905. 00000 - "missing keyword"
This is my code:
SELECT SUM(Selling_Price*Quantity_Sold)
INTO V_Today_Sale
FROM Bill_Item BI, Bill B
WHERE BI.Bill_Number = B.Bill_Number AND
Menu_Item_Number = 1 AND
Bill_Date = sysdate AND
(NVL(Paid_YN,'N') = 'Y' OR NVL(Posted_YN,'N') = 'Y')
GROUP BY Menu_Item_Number
ORDER BY Menu_Item_Number;
If I remove the variable assignment
SELECT SUM(Selling_Price*Quantity_Sold)
FROM Bill_Item BI, Bill B
WHERE BI.Bill_Number = B.Bill_Number AND
Menu_Item_Number = 1 AND
Bill_Date = sysdate AND
(NVL(Paid_YN,'N') = 'Y' OR NVL(Posted_YN,'N') = 'Y')
GROUP BY Menu_Item_Number
ORDER BY Menu_Item_Number;
the result will be:
no rows selected
It's correct since no sale has been made for today yet. But how can I make the query return 0 instead of no rows selected so that I can assign it to the variable?

Answer 1

Are you running the query as shown to test without putting it in a block (using PL/SQL or Toad)? If so, you need to define the variable and structure like this, with a call to NVL() around the SUM() call so V_Today_Sale gets a value if both inputs to SUM() are NULL, and add an exception to catch the NO_DATA_FOUND condition that sets V_Today_Sale to 0 if the where clause conditions are not met:
SET SERVEROUTPUT ON;
DECLARE
V_Today_Sale number := 0;
BEGIN
SELECT NVL(SUM(Selling_Price*Quantity_Sold), 0)
INTO V_Today_Sale
FROM Bill_Item BI, Bill B
WHERE BI.Bill_Number = B.Bill_Number AND
Menu_Item_Number = 1 AND
Bill_Date = sysdate AND
(NVL(Paid_YN,'N') = 'Y' OR NVL(Posted_YN,'N') = 'Y')
GROUP BY Menu_Item_Number
ORDER BY Menu_Item_Number;
EXCEPTION
WHEN NO_DATA_FOUND THEN
V_Today_Sale :=0;
END;
DBMS_OUTPUT.PUT_LINE(V_Today_Sale);