**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 (s_with.ignore(pos, expected))
                {
                    if (!s_name.ignore(pos, expected))
                        return false;
                    ASTPtr ast_with_name;
                    if (!parser_string_literal.parse(pos, ast_with_name, expected))
                        return false;
                    command->with_name = ast_with_name->as<ASTLiteral &>().value.get<const String &>();
                }
            }
            else if (s_unfreeze.ignore(pos, expected))
            {
                if (s_partition.ignore(pos, expected))
                {
                    if (!parser_partition.parse(pos, command->partition, expected))
                        return false;
                    command->type = ASTAlterCommand::UNFREEZE_PARTITION;
                }
                else
                {
                    command->type = ASTAlterCommand::UNFREEZE_ALL;
                }
                
                if (s_with.ignore(pos, expected))
                {
                    if (!s_name.ignore(pos, expected))
                        return false;
                    ASTPtr ast_with_name;
                    if (!parser_string_literal.parse(pos, ast_with_name, expected))
                        return false;