ClickHouse/dbms/include/DB/Parsers/ASTTablesInSelectQuery.h

#pragma once

#include <DB/Parsers/IAST.h>


namespace DB
{

/** List of zero, single or multiple JOIN-ed tables or subqueries in SELECT query, with ARRAY JOINs and SAMPLE, FINAL modifiers.
  *
  * Table expression is:
  *  [database_name.]table_name
  * or
  *  table_function(params)
  * or
  *  (subquery)
  *
  * Optionally with alias (correllation name):
  *  [AS] alias
  *
  * Table may contain FINAL and SAMPLE modifiers:
  *  FINAL
  *  SAMPLE 1 / 10
  *  SAMPLE 0.1
  *  SAMPLE 1000000
  *
  * Table expressions may be combined with JOINs of following kinds:
  *  [GLOBAL] [ANY|ALL|] INNER|LEFT|RIGHT|FULL [OUTER] JOIN table_expr
  *  CROSS JOIN
  *  , (comma)
  *
  * In all kinds except cross and comma, there are join condition in one of following forms:
  *  USING (a, b c)
  *  USING a, b, c
  *  ON expr...
  *
  * Also, tables may be ARRAY JOIN-ed with one or more arrays or nested columns:
  *  [LEFT|INNER|] ARRAY JOIN name [AS alias], ...
  */


/// Table expression, optionally with alias.
struct ASTTableExpression : public IAST
{
	/// One of fields is non-nullptr.
	ASTPtr database_and_table_name;
	ASTPtr table_function;
	ASTPtr subquery;

	/// Modifiers
	bool final = false;
	ASTPtr sample_size;
	ASTPtr sample_offset;

	using IAST::IAST;
	String getID() const override { return "TableExpression"; }
	ASTPtr clone() const override;
	void formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const override;
};


/// How to JOIN another table.
struct ASTTableJoin : public IAST
{
	/// Algorithm for distributed query processing.
	enum class Locality
	{
		Unspecified,
		Local,	/// Perform JOIN, using only data available on same servers (co-located data).
		Global	/// Collect and merge data from remote servers, and broadcast it to each server.
	};

	/// Allows more optimal JOIN for typical cases.
	enum class Strictness
	{
		Unspecified,
		Any,	/// If there are many suitable rows to join, use any from them (also known as unique JOIN).
		All		/// If there are many suitable rows to join, use all of them and replicate rows of "left" table (usual semantic of JOIN).
	};

	/// Join method.
	enum class Kind
	{
		Inner,	/// Leave ony rows that was JOINed.
		Left,	/// If in "right" table there is no corresponding rows, use default values instead.
		Right,
		Full,
		Cross,	/// Direct product. Strictness and condition doesn't matter.
		Comma	/// Same as direct product. Intended to be converted to INNER JOIN with conditions from WHERE.
	};

	Locality locality = Locality::Unspecified;
	Strictness strictness = Strictness::Unspecified;
	Kind kind = Kind::Inner;

	/// Condition. One of fields is non-nullptr.
	ASTPtr using_expression_list;
	ASTPtr on_expression;

	using IAST::IAST;
	String getID() const override { return "TableJoin"; }
	ASTPtr clone() const override;

	void formatImplBeforeTable(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const;
	void formatImplAfterTable(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const;
	void formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const override;
};


/// Specification of ARRAY JOIN.
struct ASTArrayJoin : public IAST
{
	enum class Kind
	{
		Inner,	/// If array is empty, row will not present (default).
		Left,	/// If array is empty, leave row with default values instead of array elements.
	};

	Kind kind = Kind::Inner;

	/// List of array or nested names to JOIN, possible with aliases.
	ASTPtr expression_list;

	using IAST::IAST;
	String getID() const override { return "ArrayJoin"; }
	ASTPtr clone() const override;
	void formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const override;
};


/// Element of list.
struct ASTTablesInSelectQueryElement : public IAST
{
	/** For first element of list, either table_expression or array_join element could be non-nullptr.
	  * For former elements, either table_join and table_expression are both non-nullptr, or array_join is non-nullptr.
	  */
	ASTPtr table_join;			/// How to JOIN a table, if table_expression is non-nullptr.
	ASTPtr table_expression;	/// Table, first in list or JOINed.
	ASTPtr array_join;			/// Arrays to JOIN.

	using IAST::IAST;
	String getID() const override { return "TablesInSelectQueryElement"; }
	ASTPtr clone() const override;
	void formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const override;
};


/// The list. Elements are in 'children' field.
struct ASTTablesInSelectQuery : public IAST
{
	using IAST::IAST;
	String getID() const override { return "TablesInSelectQuery"; }
	ASTPtr clone() const override;
	void formatImpl(const FormatSettings & settings, FormatState & state, FormatStateStacked frame) const override;
};


}