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.

for (auto & index : metadata.secondary_indices)
            rename_visitor.visit(index.definition_ast);
    }
    else
        throw Exception("Wrong parameter type in ALTER query", ErrorCodes::LOGICAL_ERROR);
}
bool AlterCommand::isModifyingData(const StorageInMemoryMetadata & metadata) const
{
    
    if (type == MODIFY_COLUMN)
    {
        if (data_type == nullptr)
            return false;
        
        for (const auto & column : metadata.columns.getAllPhysical())
            if (column.name == column_name)
                return !column.type->equals(*data_type);
        return true;
    }
    return type == ADD_COLUMN  
        || type == DROP_COLUMN 
        || type == DROP_INDEX; 
}
bool AlterCommand::isSettingsAlter() const
{
    return type == MODIFY_SETTING;
}
namespace
{
bool isMetadataOnlyConversion(const IDataType * from, const IDataType * to)