Oracle 21c

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CREATE TABLE table_name ( customer, products, products_trial_status ) AS
SELECT 234253, 'A,B,C', 'false,true,false' FROM DUAL UNION ALL
SELECT 923403, 'A,C',   'true,true'        FROM DUAL UNION ALL
SELECT 123483, 'B',     'true'             FROM DUAL UNION ALL
SELECT 239874, 'B,C',   'false,false'      FROM DUAL;
4 rows affected

SELECT customer,
       COALESCE(
         SUBSTR(
           status,
           LENGTH(preceding_terms) - COALESCE(LENGTH(REPLACE(preceding_terms, ',')), 0),
           1
         ),
         '0'
       ) AS hasB
FROM   (
  SELECT customer,
         SUBSTR(','||products, 1, INSTR(','||products||',', ',B,')) AS preceding_terms,
         TRANSLATE(products_trial_status, 'tfrueals,', '10') AS status
  FROM   table_name
  WHERE  INSTR(','||products||',', ',B,') > 0
)


CUSTOMER
HASB


234253
1

123483
1

239874
0


CREATE TABLE table_name ( customer, products, products_trial_status ) AS
SELECT 234253, 'A,B,C', 'false,true,false' FROM DUAL UNION ALL
SELECT 923403, 'A,C',   'true,true'        FROM DUAL UNION ALL
SELECT 123483, 'B',     'true'             FROM DUAL UNION ALL
SELECT 239874, 'B,C',   'false,false'      FROM DUAL;
ORA-00955: name is already used by an existing object

SELECT customer,
       COALESCE(
         SUBSTR(
           status,
           LENGTH(preceding_terms) - COALESCE(LENGTH(REPLACE(preceding_terms, ',')), 0),
           1
         ),
         '0'
       ) AS hasB
FROM   (
  SELECT customer,
         SUBSTR(','||products, 1, INSTR(','||products||',', ',B,')) AS preceding_terms,
         TRANSLATE(products_trial_status, 'tfrueals,', '10') AS status
  FROM   table_name
)


CUSTOMER
HASB


234253
1

923403
0

123483
1

239874
0


SELECT customer
FROM   (
  SELECT customer,
         SUBSTR(','||products, 1, INSTR(','||products||',', ',B,')) AS preceding_terms,
         TRANSLATE(products_trial_status, 'tfrueals,', '10') AS status
  FROM   table_name
  WHERE  INSTR(','||products||',', ',B,') > 0
)
WHERE   SUBSTR(
           status,
           LENGTH(preceding_terms) - COALESCE(LENGTH(REPLACE(preceding_terms, ',')), 0),
           1
         ) = '1'


CUSTOMER


234253

123483