nested_join.h

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#ifndef SQL_NESTED_JOIN_INCLUDED
#define SQL_NESTED_JOIN_INCLUDED
 
#include <sys/types.h>
#include "my_inttypes.h"
#include "my_table_map.h"
#include "sql/handler.h"
#include "sql/sql_list.h"
#include "sql/sql_opt_exec_shared.h"
 
class Item;
class Item_field;
struct POSITION;
class Table_ref;
 
/*
  Used to identify NESTED_JOIN structures within a join (applicable to
  structures representing outer joins that have not been simplified away).
*/
typedef ulonglong nested_join_map;
 
/**
  Semijoin_mat_optimize collects data used when calculating the cost of
  executing a semijoin operation using a materialization strategy.
  It is used during optimization phase only.
*/
 
struct Semijoin_mat_optimize {
  /// Optimal join order calculated for inner tables of this semijoin op.
  POSITION *positions{nullptr};
  /// True if data types allow the MaterializeLookup semijoin strategy
  bool lookup_allowed{false};
  /// True if data types allow the MaterializeScan semijoin strategy
  bool scan_allowed{false};
  /// Expected number of rows in the materialized table
  double expected_rowcount{0.0};
  /// Materialization cost - execute sub-join and write rows to temp.table
  Cost_estimate materialization_cost;
  /// Cost to make one lookup in the temptable
  Cost_estimate lookup_cost;
  /// Cost of scanning the materialized table
  Cost_estimate scan_cost;
  /// Array of pointers to fields in the materialized table.
  Item_field **mat_fields{nullptr};
};
 
/**
  Struct NESTED_JOIN is used to represent how tables are connected through
  outer join operations and semi-join operations to form a query block.
  Out of the parser, inner joins are also represented by NESTED_JOIN
  structs, but these are later flattened out by simplify_joins().
  Some outer join nests are also flattened, when it can be determined that
  they can be processed as inner joins instead of outer joins.
*/
struct NESTED_JOIN {
  NESTED_JOIN()
      : m_tables(*THR_MALLOC),
        sj_outer_exprs(*THR_MALLOC),
        sj_inner_exprs(*THR_MALLOC) {}
 
  /// list of tables referenced in the nested join
  mem_root_deque<Table_ref *> m_tables;
  table_map used_tables{0};     /* bitmap of tables in the nested join */
  table_map not_null_tables{0}; /* tables that rejects nulls           */
  /**
    Used for pointing out the first table in the plan being covered by this
    join nest. It is used exclusively within make_outerjoin_info().
  */
  plan_idx first_nested{0};
  /**
    Set to true when natural join or using information has been processed.
  */
  bool natural_join_processed{false};
  /**
    Number of tables and outer join nests administered by this nested join
    object for the sake of cost analysis. Includes direct member tables as
    well as tables included through semi-join nests, but notice that semi-join
    nests themselves are not counted.
  */
  uint nj_total{0};
  /**
    Used to count tables in the nested join in 2 isolated places:
    1. In make_outerjoin_info().
    2. check_interleaving_with_nj/backout_nj_state (these are called
       by the join optimizer.
    Before each use the counters are zeroed by Query_block::reset_nj_counters.
  */
  uint nj_counter{0};
  /**
    Bit identifying this nested join. Only nested joins representing the
    outer join structure need this, other nests have bit set to zero.
  */
  nested_join_map nj_map{0};
  /**
    Tables outside the semi-join that are used within the semi-join's
    ON condition (ie. the subquery WHERE clause and optional IN equalities).
    Also contains lateral dependencies from materialized derived tables
    contained inside the semi-join inner tables.
  */
  table_map sj_depends_on{0};
  /**
    Outer non-trivially correlated tables, a true subset of sj_depends_on.
    Also contains lateral dependencies from materialized derived tables
    contained inside the semi-join inner tables.
  */
  table_map sj_corr_tables{0};
  /**
    Query block id if this struct is generated from a subquery transform.
  */
  uint query_block_id{0};
 
  /// Bitmap of which strategies are enabled for this semi-join nest
  uint sj_enabled_strategies{0};
 
  /*
    Lists of trivially-correlated expressions from the outer and inner tables
    of the semi-join, respectively.
  */
  mem_root_deque<Item *> sj_outer_exprs, sj_inner_exprs;
  Semijoin_mat_optimize sjm;
};
 
#endif  // SQL_NESTED_JOIN_INCLUDED