Issue in adding decimal values stored as varchar - sql

Question

I have a staging table with two amount columns, created as varchar2 types to allow import from excel. Later these fields are validated to make sure they contains numeric data & summation of values for each row should greater than zero, before making the updates to actual table.
I have a function to validate whether the column contains any non numeric data, which works as expected.
FUNCTION f_isnumber (pin_string IN VARCHAR2)
RETURN INT
IS
v_new_num NUMBER;
BEGIN
IF TRIM (pin_string) IS NOT NULL
THEN
v_new_num := TO_NUMBER (pin_string);
RETURN 1;
END IF;
RETURN 0;
EXCEPTION
WHEN VALUE_ERROR
THEN
RETURN 0;
END f_isnumber;
Next is I wanted to list all the rows where value of two amount field is zero. Below query works where I am just selecting the total of both columns.
WITH CTE1
AS (SELECT TO_NUMBER (PURCH_AMT) + TO_NUMBER (SELL_AMT) AS Total, ROW_ID
FROM STG_MAINTENANCE
WHERE PKG_MAINTENANCE.f_isnumber (PURCH_AMT) > 0
AND PKG_MAINTENANCE.f_isnumber (SELL_AMT) > 0)
SELECT TO_NUMBER (Total), CTE1.*
FROM CTE1
But as soon as I add where clause, the query fails with error "ORA-01722: invalid number"
WITH CTE1
AS (SELECT TO_NUMBER (PURCH_AMT) + TO_NUMBER (SELL_AMT) AS Total, ROW_ID
FROM STG_MAINTENANCE
WHERE PKG_MAINTENANCE.f_isnumber (PURCH_AMT) > 0
AND PKG_MAINTENANCE.f_isnumber (SELL_AMT) > 0)
SELECT TO_NUMBER (Total), CTE1.*
FROM CTE1
WHERE Total = 0
Table contains both valid numbers, spaces & valid decimals, zero etc. I was hoping inner where clause will eliminate all non numeric values & I would only get valid decimal values & if user has imported 0 or 0.00
But somehow invalid number error comes up.
Sample Data:
Create table STG_MAINTENANCE (ROW_ID INT, PURCH_AMT VARCHAR2(500), SELL_AMT VARCHAR2(500));
INSERT INTO STG_MAINTENANCE values(1, 'A','4.5');
INSERT INTO STG_MAINTENANCE values(2, '0','0.0');
INSERT INTO STG_MAINTENANCE values(3, '5.5','4.5');
INSERT INTO STG_MAINTENANCE values(4, '','4.5');
INSERT INTO STG_MAINTENANCE values(5, 'B','C');
INSERT INTO STG_MAINTENANCE values(6, '','');

Answer 1

I think The way Oracle is processing your query causes the error in your query.
For your example, You can use MATERIALIZE hint and write your query like the following:
WITH CTE1 AS (
SELECT /*+MATERIALIZE*/
TO_NUMBER(PURCH_AMT) + TO_NUMBER(SELL_AMT) AS TOTAL,
ROW_ID
FROM
STG_MAINTENANCE
WHERE
PKG_MAINTENANCE.F_ISNUMBER(PURCH_AMT) > 0
AND PKG_MAINTENANCE.F_ISNUMBER(SELL_AMT) > 0
)
SELECT
TO_NUMBER(TOTAL),
CTE1.*
FROM
CTE1
WHERE
TOTAL = 0
You can learn more about MATERIALIZE hint from oracle docs.
Hope this is helpful to you.