PL/SQL key-value String using Regex - regex

Question

I have a String stored in a table in the following key-value format: "Key1☺Value1☺Key2☺Value2☺KeyN☺ValueN☺".
Given a Key how can I extract the Value? Is regex the easiest way to handle this? I am new to PL/SQL as well as Regex.

Answer 1

In this case, I would use just a regular split and iterate through the resulting array.
public string GetValue(string keyValuePairedInput, string key, char separator)
{
var split = keyValuePairedInput.Split(separator);
if(split.Lenght % 2 == 1)
throw new KeyWithoutValueException();
for(int i = 0; i < split.Lenght; i += 2)
{
if(split[i] == key)
return split[i + 1];
}
throw new KeyNotFoundException();
}
(this was not compiled and is not pl/sql anyway, treat it as pseudocode ☺)
OK I hear your comment...
Making use of pl/sql functions, you might be able to use something like this:
select 'key' as keyValue,
(instr(keyValueStringField, keyValue) + length(keyValue) + 1) as valueIndex,
substr(keyValueStringField, valueIndex, instr(keyValueStringField, '\1', valueIndex) - valueIndex) as value
from Table

Answer 2

For this kind of string slicing and dicing in PL/SQL you will probably have to use regular expressions. Oracle has a number of regular expression functions you can use. The most commonly used one is REGEXP_LIKE which is very similar to the LIKE operator but does RegEx matching.
However you probably need to use REGEXP_INSTR to find the positions where the separators are then use the SUBSTR function to slice up the string at the matched positions. You could also consider using REGEXP_SUBSTR which does the RegEx matching and slicing in one step.

Answer 3

As an alternative to regular expressions...
Assuming you have an input such as this:
Key1,Value1|Key2,Value2|Key3,Value3
You could use some PL/SQL as shown below:
FUNCTION get_value_by_key
(
p_str VARCHAR2
, p_key VARCHAR2
, p_kvp_separator VARCHAR2
, p_kv_separator VARCHAR2
) RETURN VARCHAR2
AS
v_key VARCHAR2(32767);
v_value VARCHAR2(32767);
v_which NUMBER;
v_cur VARCHAR(1);
BEGIN
v_which := 0;
FOR i IN 1..length(p_str)
LOOP
v_cur := substr(p_str,i,1);
IF v_cur = p_kvp_separator
THEN
IF v_key = p_key
THEN
EXIT;
END IF;
v_key := '';
v_value := '';
v_which := 0;
ELSIF v_cur = p_kv_separator
THEN
v_which := 1;
ELSE
IF v_which = 0
THEN
v_key := v_key || v_cur;
ELSE
v_value := v_value || v_cur;
END IF;
END IF;
END LOOP;
IF v_key = p_key
THEN
RETURN v_value;
END IF;
raise_application_error(-20001, 'key not found!');
END;
To get the value for 'Key2' you could do this (assuming your function was in a package called test_pkg):
SELECT test_pkg.get_value_by_key('Key1,Value1|Key2,Value2|Key3,Value3','Key2','|',',') FROM dual