**Use case**

PostgreSQL is using `ALTER TABLE t ALTER COLUMN c TYPE type` instead of `ALTER TABLE t MODIFY COLUMN c type`.
There is a risk that some people already get used to PostgreSQL syntax.

Let's implement it in ClickHouse.

```
tutorial=# ALTER TABLE hits_100m_obfuscated MODIFY COLUMN UserAgentMinor TEXT
tutorial-# ;
ERROR:  syntax error at or near "MODIFY"
LINE 1: ALTER TABLE hits_100m_obfuscated MODIFY COLUMN UserAgentMino...
                                         ^
tutorial=# ALTER TABLE hits_100m_obfuscated ALTER COLUMN UserAgentMinor TYPE TEXT
;
ALTER TABLE
tutorial=#
```

**Proposed implementation**

Implement it in parser level.
{
                    if (!parser_partition.parse(pos, command->partition, expected))
                        return false;
                }
            }
            else if (s_add_index.ignore(pos, expected))
            {
                if (s_if_not_exists.ignore(pos, expected))
                    command->if_not_exists = true;
                if (!parser_idx_decl.parse(pos, command->index_decl, expected))
                    return false;
                if (s_first.ignore(pos, expected))
                    command->first = true;
                else if (s_after.ignore(pos, expected))
                {
                    if (!parser_name.parse(pos, command->index, expected))
                        return false;
                }
                command->type = ASTAlterCommand::ADD_INDEX;
            }
            else if (s_drop_index.ignore(pos, expected))
            {
                if (s_if_exists.ignore(pos, expected))
                    command->if_exists = true;
                if (!parser_name.parse(pos, command->index, expected))
                    return false;
                command->type = ASTAlterCommand::DROP_INDEX;
                command->detach = false;
            }
            else if (s_clear_index.ignore(pos, expected))