**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.
#include <Common/typeid_cast.h>
#include <Parsers/ParserAlterQuery.h>
#include <Parsers/CommonParsers.h>
#include <Parsers/ExpressionElementParsers.h>
#include <Parsers/ExpressionListParsers.h>
#include <Parsers/ParserCreateQuery.h>
#include <Parsers/ParserPartition.h>
#include <Parsers/ParserSelectWithUnionQuery.h>
#include <Parsers/ParserSetQuery.h>
#include <Parsers/ASTIdentifier.h>
#include <Parsers/ASTIndexDeclaration.h>
#include <Parsers/ASTAlterQuery.h>
#include <Parsers/ASTLiteral.h>
#include <Parsers/parseDatabaseAndTableName.h>
namespace DB
{
bool ParserAlterCommand::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)