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.

if (!after_index_name.empty())
        {
            insert_it = std::find_if(
                    metadata.secondary_indices.begin(),
                    metadata.secondary_indices.end(),
                    [this](const auto & index)
                    {
                        return index.name == after_index_name;
                    });
            if (insert_it == metadata.secondary_indices.end())
                throw Exception("Wrong index name. Cannot find index " + backQuote(after_index_name) + " to insert after.",
                        ErrorCodes::BAD_ARGUMENTS);
            ++insert_it;
        }
        metadata.secondary_indices.emplace(insert_it, IndexDescription::getIndexFromAST(index_decl, metadata.columns, context));
    }
    else if (type == DROP_INDEX)
    {
        if (!partition && !clear)
        {
            auto erase_it = std::find_if(
                    metadata.secondary_indices.begin(),
                    metadata.secondary_indices.end(),
                    [this](const auto & index)
                    {
                        return index.name == index_name;
                    });
            if (erase_it == metadata.secondary_indices.end())
            {
                if (if_exists)