Присоединяйтесь к SQL на запятой отдельно
SELECT * FROM `TABLE1`
JOIN `TABLE2` ON `TABLE1`.`id` = `TABLE2`.`COMMA_SEPERATED_COLUMN`
AND `TABLE2`.`COMMA_SEPERATED_COLUMN` REGEXP "(^|,)SPECIFIC_ID(,|$)"
############## OR #######################
SELECT * FROM table1
LEFT JOIN table2 ast ON ast.nodeid = c_NodeId
AND ',' + ast.GroupNames + ',' LIKE '%,' + table1.GroupAlphabet + ',%';
Lokesh003