Trying to update substrings in SQL - sql

Question

Can anyone help with some SQL syntax?
I have a table (TABLE A) which contains a 54 character field (FIELD A) which in essence contains 8x6 blocks of data.
These can be broken down into substrings:
substr(FIELD A,1,6) as A
substr(FIELD A,7,6) as B
substr(FIELD A,13,6) as C
substr(FIELD A,19,6) as D
substr(FIELD A,25,6) as E
substr(FIELD A,31,6) as F
substr(FIELD A,37,6) as G
substr(FIELD A,43,6) as H
substr(FIELD A,49,6) as I
What I need to do is if there an occurrence of '404040' in any of these substring fields (A to I), replace them with '000000'. The '404040' has to be in these exact positions, not just a 'like %404040%' anywhere in FIELD A. I don't think I can perform an Update on a substring(?) but my efforts at using the Replace haven't yet worked. Can anyone suggest a solution?
I'm using SQL Developer 3.2.20.10 and Oracle 12.
Many Thanks AP

Answer 1

You can achieve this using two functions Replacepos to replace the string at the position and replacepos1 to mention the no_of_chars to be replaced.After that you can just use the below SQL
WITH data
AS (SELECT ROWNUM rw,
Lpad('404040', 54, '404040') A
FROM dual),
d1
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 1, Replacepos1(a, '0', 1, 6)) A
FROM data),
d2
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 7, Replacepos1(a, '0', 7, 6)) A
FROM d1),
d3
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 13, Replacepos1(a, '0', 13, 6))A
FROM d2),
d4
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 19, Replacepos1(a, '0', 19, 6))A
FROM d3),
d5
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 25, Replacepos1(a, '0', 25, 6))A
FROM d4),
d6
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 31, Replacepos1(a, '0', 31, 6))A
FROM d5),
d7
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 37, Replacepos1(a, '0', 37, 6))A
FROM d6),
d8
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 43, Replacepos1(a, '0', 43, 6))A
FROM d7),
d9
AS (SELECT rw,
Decode(Instr(a, '404040', 1), 49, Replacepos1(a, '0', 49, 6))A
FROM d8)
SELECT A
FROM d9;
The Functions specifications below
CREATE OR replace FUNCTION Replacepos(source_in IN VARCHAR2,
replacechar_in IN VARCHAR2,
position_start IN NUMBER)
RETURN VARCHAR2
IS
l_returnvalue VARCHAR2(32767);
position_in NUMBER;
BEGIN
-- copy from the source string up to, but not including,
-- the character position
position_in := position_start;
-- to be replaced
l_returnvalue := Substr(str1 => source_in, pos => 1, len => position_in - 1)
;
-- add the replacement character
-- just a single character, but more can be sent in,
-- so substring the parameter
l_returnvalue := l_returnvalue
|| Substr(str1 => replacechar_in, pos => 1, len => 1);
-- copy the rest of the source string
l_returnvalue := l_returnvalue
|| Substr(str1 => source_in, pos => position_in + 1);
RETURN l_returnvalue;
END replacepos;
AND the below function
CREATE OR replace FUNCTION Replacepos1 (source_in IN VARCHAR2,
replacechar_in IN VARCHAR2,
position_start IN NUMBER,
no_of_chars IN NUMBER)
RETURN VARCHAR2
IS
l_returnvalue VARCHAR2(32767);
position_in NUMBER;
BEGIN
l_returnvalue := source_in;
FOR i IN 1..no_of_chars LOOP
l_returnvalue := Replacepos(l_returnvalue, replacechar_in,
position_start + i - 1);
END LOOP;