sql_union.h

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/* Copyright (c) 2006, 2025, Oracle and/or its affiliates.
 
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   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
   You should have received a copy of the GNU General Public License
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef SQL_UNION_INCLUDED
#define SQL_UNION_INCLUDED
 
#include <sys/types.h>
 
#include "my_inttypes.h"
#include "sql/query_result.h"  // Query_result_interceptor
#include "sql/table.h"
#include "sql/temp_table_param.h"  // Temp_table_param
 
class Item;
class Query_expression;
class THD;
template <class Element_type>
class mem_root_deque;
 
class Query_result_union : public Query_result_interceptor {
 protected:
  Temp_table_param tmp_table_param;
 
 public:
  TABLE *table;
 
  Query_result_union() : Query_result_interceptor(), table(nullptr) {}
  bool prepare(THD *thd, const mem_root_deque<Item *> &list,
               Query_expression *u) override;
  /**
    Do prepare() if preparation has been postponed until column type
    information is computed (used by Query_result_union_direct).
 
    @param thd   Thread handle
    @param types Column types
 
    @return false on success, true on failure
  */
  virtual bool postponed_prepare(THD *thd [[maybe_unused]],
                                 const mem_root_deque<Item *> &types
                                 [[maybe_unused]]) {
    return false;
  }
  bool send_data(THD *thd, const mem_root_deque<Item *> &items) override;
  bool send_eof(THD *thd) override;
  virtual bool flush();
  void cleanup() override { (void)reset(); }
  bool reset() override;
  bool create_result_table(THD *thd, const mem_root_deque<Item *> &column_types,
                           bool is_distinct, ulonglong options,
                           const char *alias, bool create_table,
                           Query_term_set_op *op = nullptr);
  friend bool Table_ref::create_materialized_table(THD *thd);
  friend bool Table_ref::optimize_derived(THD *thd);
  uint get_hidden_field_count() const {
    return tmp_table_param.hidden_field_count;
  }
  bool skip_create_table() const { return tmp_table_param.skip_create_table; }
 
  /// Set an effective LIMIT for the number of rows coming out of a materialized
  /// temporary table used for implementing INTERSECT or EXCEPT: informs
  /// TableScanIterator::TableScanIterator how many rows to read from the
  /// materialized table. For UNION and simple tables the limitation is enforced
  /// earlier, at materialize time, but this is not possible for INTERSECT and
  /// EXCEPT due to the use of cardinality counters.
  ///
  /// @param limit_rows the effective limit, or HA_POS_ERROR if none.
  void set_limit(ha_rows limit_rows) override;
 
  // For assignment of tmp_table_param for CTE clones
  friend class Common_table_expr;
};
 
#endif /* SQL_UNION_INCLUDED */