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.

}
void AlterCommand::apply(StorageInMemoryMetadata & metadata, const Context & context) const
{
    if (type == ADD_COLUMN)
    {
        ColumnDescription column(column_name, data_type);
        if (default_expression)
        {
            column.default_desc.kind = default_kind;
            column.default_desc.expression = default_expression;
        }
        if (comment)
            column.comment = *comment;
        column.codec = codec;
        column.ttl = ttl;
        metadata.columns.add(column, after_column, first);
        
        metadata.columns.flattenNested();
    }
    else if (type == DROP_COLUMN)
    {
        
        if (!clear && !partition)
            metadata.columns.remove(column_name);
    }
    else if (type == MODIFY_COLUMN)
    {
        metadata.columns.modify(column_name, after_column, first, [&](ColumnDescription & column)
        {
            if (codec)