Oracle REGEXP_LIKE logical and matching of substrings in string

Question

I have a string containing codes like 'code1 code2 code3'. It should return the string if all codes entered are contained in the string.

For example:

select * from (
select 'avs cde jkl' code from dual)
where REGEXP_LIKE(code, 'REGEX-MAGIC') 

When the regex is now something like ^(?=.*\bjkl\b)(?=.*\bavs\b).*$ then it should return the code. But this syntax is not working for regex in oracle.

The logic is 'if all codes looked for are in the string (order does not matter), then return the code.'

I have researched and this would be achievable with a positive lookahead, but oracle does not support this as far as I know. I would search for one regex and not a construct like REGEXP_LIKE(...,..) and REGEXP_LIKE(...,..) and ....

The Oracle Version is 12c.

Any help would be appreciated!

Answer 1

Oracle does not support look-ahead, look-behind or word boundaries in regular expressions.

If you have the sample data:

CREATE TABLE table_name (code) AS
SELECT 'avs cde jkl' FROM DUAL UNION ALL
SELECT 'avs cde'     FROM DUAL UNION ALL
SELECT 'jkl avs'     FROM DUAL UNION ALL
SELECT 'cde jkl'     FROM DUAL;

Option 1:

The simplest query is to not use regular expressions and to look for sub-string matches using multiple LIKE conditions:

SELECT code
FROM   table_name
WHERE  ' ' || code || ' ' LIKE '% avs %'
AND    ' ' || code || ' ' LIKE '% jkl %'

Which outputs:

CODE
avs cde jkl
jkl avs

Option 2:

You could use (slower) regular expressions with multiple REGEXP_LIKE conditions:

SELECT code
FROM   table_name
WHERE  REGEXP_LIKE(code, '(^| )avs( |$)')
AND    REGEXP_LIKE(code, '(^| )jkl( |$)')

Which outputs the same as above.

Option 3:

You could put the matches into a sub-query factoring clause and then use a LATERAL join:

WITH match_conditions (match) AS (
  SELECT 'avs' FROM DUAL UNION ALL
  SELECT 'jkl' FROM DUAL
)
SELECT code
FROM   table_name t
       CROSS JOIN LATERAL (
         SELECT 1
         FROM   match_conditions
         WHERE  ' ' || code || ' ' LIKE '% ' || match || ' %'
         HAVING COUNT(*) = (SELECT COUNT(*) FROM match_conditions)
       )

Which outputs the same as above.

Option 4:

If you really want a single regular expression then you can generate each permutation of the codes to match and concatenate them into a single regular expression:

SELECT code
FROM   table_name
WHERE  REGEXP_LIKE(
         code,
             '(^| )avs( | .*? )jkl( |$)' -- Permutation 1
         || '|(^| )jkl( | .*? )avs( |$)' -- Permutation 2
       )

Which outputs the same as above.

However, this is going to get problematic to maintain as the number of codes to match grows as, for 2 items there are 2 permutations but for 5 items there are 5! = 120 permutations.

Option 5:

You could declare a nested table collection:

CREATE TYPE string_list AS TABLE OF VARCHAR2(20);

Then split the string (again, you do not need slow regular expressions) and then compare it to a nested table:

WITH bounds (rid, code, spos, epos) AS (
  SELECT ROWID, code, 1, INSTR(code, ' ', 1)
  FROM   table_name
UNION ALL
  SELECT rid, code, epos + 1, INSTR(code, ' ', epos + 1)
  FROM   bounds
  WHERE  epos > 0
)
SEARCH DEPTH FIRST BY code SET order_rn
SELECT MAX(code) AS code
FROM   bounds
GROUP BY rid
HAVING string_list('avs', 'jkl') SUBMULTISET OF CAST(
         COLLECT(
           CAST(
             CASE epos
             WHEN 0
             THEN SUBSTR(code, spos)
             ELSE SUBSTR(code, spos, epos - spos)
             END
             AS VARCHAR2(20)
           )
         )
         AS string_list
       );

Depending on the client application you are using, you can pass the entire string_list('avs', 'jkl') collection in as a single bind variable that you can populate from an array. Java (and some languages built on top of Java) using an ODBC driver can do this; C# cannot directly but you can pass an associative array and convert it to a nested table collection with a helper function.

Which outputs the same as above.

db<>fiddle here