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.

primary_key = KeyDescription::getKeyFromAST(sorting_key.definition_ast, metadata.columns, context);
        }
        
        sorting_key.recalculateWithNewAST(order_by, metadata.columns, context);
    }
    else if (type == COMMENT_COLUMN)
    {
        metadata.columns.modify(column_name,
            [&](ColumnDescription & column) { column.comment = *comment; });
    }
    else if (type == ADD_INDEX)
    {
        if (std::any_of(
                metadata.secondary_indices.cbegin(),
                metadata.secondary_indices.cend(),
                [this](const auto & index)
                {
                    return index.name == index_name;
                }))
        {
            if (if_not_exists)
                return;
            else
                throw Exception{"Cannot add index " + index_name + ": index with this name already exists",
                                ErrorCodes::ILLEGAL_COLUMN};
        }
        auto insert_it = metadata.secondary_indices.end();