Why this regexp in Oracle SQL loses the beginning of string? - sql

Question

I'm splitting a string p_value using p_delimeter, which may contain one or more symbols (that's why regexp is not like often used [^,]+).
In most of the cases the following query works predictably, but I'm dazed with a case when:
string p_value contains line break chr(10),
p_value doesn't contain p_delimeter as substring,
so I expect to have one row with the whole p_value as the result, but got only the remainder after line break.
It's supposed here that regexp treats line break as ordinary symbol, since
the 'm' modifier is absent in call to regexp_substr.
Please, explain is this behavior correct and how to get the expected result.
WITH
params AS (SELECT 'ab' || chr(10) || 'cd' p_value,
'xxx' p_delimeter
FROM dual
)
SELECT regexp_substr(p_value, '(.*?)(' || p_delimeter || '|$)', 1, level, 'c', 1) AS CUT
FROM params
CONNECT BY regexp_substr(p_value, '(.*?)(' || p_delimeter || '|$)', 1, level, 'c', 1) IS NOT NULL;
Actual result: Expected result:
----- ------
CUT CUT
----- ------
cd ab/cd
^
'this is just a marker for a line break [= chr(10)]'

Answer 1

Allow the . pattern to match all characters by adding the n flag to the regular expression:
WITH params ( p_value, p_delimiter ) AS (
SELECT 'ab' || chr(10) || 'cd', 'xxx' FROM dual
)
SELECT REGEXP_SUBSTR(p_value, '(.*?)(' || p_delimeter || '|$)', 1, level, 'cn', 1) AS CUT
FROM params
CONNECT BY LEVEL < REGEXP_COUNT( p_value, '(.*?)(' || p_delimeter || '|$)' );
or you can use a simple function:
Oracle Setup:
CREATE TYPE VARCHAR2_TABLE AS TABLE OF VARCHAR2(4000);
/
CREATE OR REPLACE FUNCTION split_String(
i_str IN VARCHAR2,
i_delim IN VARCHAR2 DEFAULT ','
) RETURN VARCHAR2_TABLE DETERMINISTIC
AS
p_result VARCHAR2_TABLE := VARCHAR2_TABLE();
p_start NUMBER(5) := 1;
p_end NUMBER(5);
c_len CONSTANT NUMBER(5) := LENGTH( i_str );
c_ld CONSTANT NUMBER(5) := LENGTH( i_delim );
BEGIN
IF c_len > 0 THEN
p_end := INSTR( i_str, i_delim, p_start );
WHILE p_end > 0 LOOP
p_result.EXTEND;
p_result( p_result.COUNT ) := SUBSTR( i_str, p_start, p_end - p_start );
p_start := p_end + c_ld;
p_end := INSTR( i_str, i_delim, p_start );
END LOOP;
IF p_start <= c_len + 1 THEN
p_result.EXTEND;
p_result( p_result.COUNT ) := SUBSTR( i_str, p_start, c_len - p_start + 1 );
END IF;
END IF;
RETURN p_result;
END;
/
Query:
WITH params ( p_value, p_delimiter ) AS (
SELECT 'ab' || chr(10) || 'cd', 'xxx' FROM dual
)
SELECT COLUMN_VALUE AS CUT
FROM params,
TABLE( split_String( p_value, p_delimiter ) );