splitByChar Nullable - sql

Question

I have the next query:
SELECT DISTINCT col_name, toTypeName(col_name)
FROM remote('host_name', 'db.table', 'user', 'password')
The result is a 6 records(WITHOUT NULL). Example:
some_prefix-1, Nullable(String)
...
some_prefix-6, Nullable(String)
Now I try splitByChar, but I'm getting:
Code: 43, e.displayText() = DB::Exception: Nested type Array(String)
cannot be inside Nullable type (version 20.1.2.4 (official build))
I tried to use not null condition and convert type but the problem still remains. Like that:
SELECT DISTINCT toString(col_name) AS col_name_str,
splitByChar('-', col_name_str)
FROM remote('host_name', 'db.table', 'user', 'password')
WHERE col_name IS NOT NULL
Is this expected behavior? How to fix this?

Answer 1

Lack of Nullable support in splitByChar (https://github.com/ClickHouse/ClickHouse/issues/6517)
You use wrong cast toString
SELECT DISTINCT
cast(col_name, 'String') AS col_name_str,
splitByChar('-', col_name_str)
FROM
(
SELECT cast('aaaaa-vvvv', 'Nullable(String)') AS col_name
)
WHERE isNotNull(col_name)
┌─col_name_str─┬─splitByChar('-', cast(col_name, 'String'))─┐
│ aaaaa-vvvv │ ['aaaaa','vvvv'] │
└──────────────┴────────────────────────────────────────────┘
or assumeNotNull
SELECT DISTINCT
assumeNotNull(col_name) AS col_name_str,
splitByChar('-', col_name_str)
FROM
(
SELECT cast('aaaaa-vvvv', 'Nullable(String)') AS col_name
)
WHERE isNotNull(col_name)
┌─col_name_str─┬─splitByChar('-', assumeNotNull(col_name))─┐
│ aaaaa-vvvv │ ['aaaaa','vvvv'] │
└──────────────┴───────────────────────────────────────────┘