Oracle 11g Release 2

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CREATE TABLE static_table(value) AS
SELECT 'GB' FROM DUAL UNION ALL
SELECT 'CH' FROM DUAL;
2 rows affected

CREATE TABLE string_from_function(function_value) AS
SELECT 'GB' FROM DUAL UNION ALL
SELECT 'CH' FROM DUAL UNION ALL
SELECT 'GB,CH' FROM DUAL UNION ALL
SELECT 'CH,GB' FROM DUAL UNION ALL
SELECT 'GB,FR' FROM DUAL UNION ALL
SELECT 'FR,ES' FROM DUAL UNION ALL
SELECT 'ES,CH' FROM DUAL UNION ALL
SELECT 'CH,GB,ES' FROM DUAL;
8 rows affected

SELECT SUBSTR(SYS_CONNECT_BY_PATH(value, ','), 2) AS combination
FROM   static_table
CONNECT BY NOCYCLE PRIOR value != value;


COMBINATION


GB

GB,CH

CH

CH,GB


SELECT function_value,
       CASE
       WHEN function_value IN (SELECT SUBSTR(SYS_CONNECT_BY_PATH(value, ','), 2)
                               FROM   static_table
                               CONNECT BY NOCYCLE
                                 PRIOR value != value)
       THEN 'false'
       ELSE 'true'
       END AS not_matched
FROM   string_from_function;


FUNCTION_VALUE
NOT_MATCHED


GB
false

CH
false

GB,CH
false

CH,GB
false

GB,FR
true

FR,ES
true

ES,CH
true

CH,GB,ES
true

FUNCTION_VALUE	NOT_MATCHED
GB	false
CH	false
GB,CH	false
CH,GB	false
GB,FR	true
FR,ES	true
ES,CH	true
CH,GB,ES	true