ClickHouse/dbms/src/Storages/AlterCommands.h

#pragma once

#include <optional>
#include <Core/NamesAndTypes.h>
#include <Storages/ColumnsDescription.h>
#include <optional>



namespace DB
{

class ASTAlterCommand;

/// Operation from the ALTER query (except for manipulation with PART/PARTITION). Adding Nested columns is not expanded to add individual columns.
struct AlterCommand
{
    enum Type
    {
        ADD_COLUMN,
        DROP_COLUMN,
        MODIFY_COLUMN,
        MODIFY_PRIMARY_KEY,
    };

    Type type;

    String column_name;

    /// For DROP COLUMN ... FROM PARTITION
    String partition_name;

    /// For ADD and MODIFY, a new column type.
    DataTypePtr data_type;

    ColumnDefaultKind default_kind{};
    ASTPtr default_expression{};

    /// For ADD - after which column to add a new one. If an empty string, add to the end. To add to the beginning now it is impossible.
    String after_column;

    /// For MODIFY_PRIMARY_KEY
    ASTPtr primary_key;

    AlterCommand() = default;
    AlterCommand(const Type type, const String & column_name, const DataTypePtr & data_type,
                 const ColumnDefaultKind default_kind, const ASTPtr & default_expression,
                 const String & after_column = String{})
        : type{type}, column_name{column_name}, data_type{data_type}, default_kind{default_kind},
        default_expression{default_expression}, after_column{after_column}
    {}

    static std::optional<AlterCommand> parse(const ASTAlterCommand * command);

    void apply(ColumnsDescription & columns_description) const;

};

class IStorage;
class Context;

class AlterCommands : public std::vector<AlterCommand>
{
public:
    void apply(ColumnsDescription & columns_description) const;

    void validate(const IStorage & table, const Context & context);
};

}