**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.
{
protected:
    const char * getName() const override { return "index declaration list"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserConstraintDeclarationList : public IParserBase
{
protected:
    const char * getName() const override { return "constraint declaration list"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserProjectionDeclarationList : public IParserBase
{
protected:
    const char * getName() const override { return "projection declaration list"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserTablePropertiesDeclarationList : public IParserBase
{
protected:
    const char * getName() const override { return "columns or indices declaration list"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
/**
  * ENGINE = name [PARTITION BY expr] [ORDER BY expr] [PRIMARY KEY expr] [SAMPLE BY expr] [SETTINGS name = value, ...]
  */
class ParserStorage : public IParserBase