You could write a udf like
my_find_in_set(k, l)
that splits comma-separated list (string) l to an array, then loops through it, looking for l.
This approach might also help:
singlestore> select json_array_contains_string('["a","b","c"]', "b");
+--------------------------------------------------+
| json_array_contains_string('["a","b","c"]', "b") |
+--------------------------------------------------+
| 1 |
+--------------------------------------------------+
1 row in set (0.19 sec)
singlestore> select json_array_contains_string('["a","b","c"]', "q");
+--------------------------------------------------+
| json_array_contains_string('["a","b","c"]', "q") |
+--------------------------------------------------+
| 0 |
+--------------------------------------------------+
Depending on the situation, you might also want to turn the list into a rowset of its items, then use SQL selects, joins or EXISTS to test for membership. E.g.:
singlestore> select * from table(split("a,b,c", ",")) where table_col = "c";
+-----------+
| table_col |
+-----------+
| c |
+-----------+
1 row in set (0.02 sec)
singlestore> select * from table(split("a,b,c", ",")) where table_col = "q";
Empty set (0.00 sec)