Newer versions can't clear columns which are used in default expressions for other columns. Maybe it's caused by https://github.com/ClickHouse/ClickHouse/issues/6913

CH version 20.5.2


create database Temp;
create table Temp.Test (`impression_id` String,`impression_id_compressed` FixedString(16) DEFAULT UUIDStringToNum(substring(impression_id, 1, 36)), `impression_id_hashed` UInt16 DEFAULT reinterpretAsUInt16(impression_id_compressed), `event_date` Date ) ENGINE = MergeTree(event_date, impression_id_hashed, (event_date, impression_id_hashed), 8192);
alter table Temp.Test clear column `impression_id` in partition '202001';


Received exception from server (version 20.5.2):
Code: 44. DB::Exception: Received from ch7r1.local:9000. DB::Exception: Cannot drop column `impression_id`, because column `impression_id_compressed` depends on it. 




Older versions (tested with 19.17.4 and 20.3.5):

CREATE DATABASE Temp;
create table Temp.Test (`impression_id` String,`impression_id_compressed` FixedString(16) DEFAULT UUIDStringToNum(substring(impression_id, 1, 36)), `impression_id_hashed` UInt16 DEFAULT reinterpretAsUInt16(impression_id_compressed), `event_date` Date ) ENGINE = MergeTree(event_date, impression_id_hashed, (event_date, impression_id_hashed), 8192);
alter table Temp.Test clear column `impression_id` in partition '202001';

ALTER TABLE Temp.Test
    CLEAR COLUMN impression_id     IN PARTITION '202001'


Ok.

{
        result.type = MutationCommand::Type::DROP_INDEX;
        result.column_name = index_name;
        if (clear)
            result.clear = true;
        if (partition)
            result.partition = partition;
        result.predicate = nullptr;
    }
    else if (type == RENAME_COLUMN)
    {
        result.type = MutationCommand::Type::RENAME_COLUMN;
        result.column_name = column_name;
        result.rename_to = rename_to;
    }
    result.ast = ast->clone();
    apply(metadata, context);
    return result;
}
String alterTypeToString(const AlterCommand::Type type)
{
    switch (type)
    {
    case AlterCommand::Type::ADD_COLUMN:
        return "ADD COLUMN";
    case AlterCommand::Type::ADD_CONSTRAINT:
        return "ADD CONSTRAINT";
    case AlterCommand::Type::ADD_INDEX:
        return "ADD INDEX";
    case AlterCommand::Type::COMMENT_COLUMN: