Split comma separated values to columns in Oracle

Question

I have values being returned with 255 comma separated values. Is there an easy way to split those into columns without having 255 substr?

ROW  | VAL
----------- 
1    | 1.25, 3.87, 2, ... 
2    | 5, 4, 3.3, ....

to

ROW | VAL | VAL | VAL ...
--------------------- 
1   |1.25 |3.87 | 2 ...     
2   | 5   | 4   | 3.3 ...

Answer 1

Beware! The regexp_substr expression of the format '[^,]+' will not return the expected value if there is a null element in the list and you want that item or one after it. Consider this example where the 4th element is NULL and I want the 5th element and thus expect the '5' to be returned:

SQL> select regexp_substr('1,2,3,,5,6', '[^,]+', 1, 5) from dual;

R
-
6

Surprise! It returns the 5th NON-NULL element, not the actual 5th element! Incorrect data returned and you may not even catch it. Try this instead:

SQL> select regexp_substr('1,2,3,,5,6', '(.*?)(,|$)', 1, 5, NULL, 1) from dual;

R
-
5

So, the above corrected REGEXP_SUBSTR says to look for the 5th occurrence of 0 or more comma-delimited characters followed by a comma or the end of the line (allows for the next separator, be it a comma or the end of the line) and when found return the 1st subgroup (the data NOT including the comma or end of the line).

The search match pattern '(.*?)(,|$)' explained:

(             = Start a group
.             = match any character
*             = 0 or more matches of the preceding character
?             = Match 0 or 1 occurrences of the preceding pattern
)             = End the 1st group
(             = Start a new group (also used for logical OR)
,             = comma
|             = OR
$             = End of the line
)             = End the 2nd group

EDIT: More info added and simplified the regex.

See this post for more info and a suggestion to encapsulate this in a function for easy reuse: REGEX to select nth value from a list, allowing for nulls It's the post where I discovered the format '[^,]+' has the problem. Unfortunately it's the regex format you will most commonly see as the answer for questions regarding how to parse a list. I shudder to think of all the incorrect data being returned by '[^,]+'!