create_field.h

#ifndef SQL_CREATE_FIELD_INCLUDED
#define SQL_CREATE_FIELD_INCLUDED

/* Copyright (c) 2018, 2026, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   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 not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
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   the program or referenced in the documentation.

   This program is distributed in the hope that it will be useful,
   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 */

#include <optional>

#include "field_types.h"
#include "lex_string.h"
#include "my_alloc.h"
#include "my_base.h"
#include "mysql/strings/m_ctype.h"
#include "sql/dd/types/column.h"
#include "sql/field.h"
#include "sql/gis/srid.h"
#include "sql/sql_list.h"
#include "typelib.h"

class Item;
class String;
class Value_generator;

/// Create_field is a description a field/column that may or may not exists in
/// a table.
///
/// The main usage of Create_field is to contain the description of a column
/// given by the user (usually given with CREATE TABLE). It is also used to
/// describe changes to be carried out on a column (usually given with ALTER
/// TABLE ... CHANGE COLUMN).
class Create_field {
 public:
  /// @returns the maximum display width of this column, in number of.
  ///          code points. See m_max_display_width_in_codepoints for an
  ///          explanation of "display width" and "code point".
  size_t max_display_width_in_codepoints() const;

  /// @returns the maximum display width of this column, in number of bytes. For
  ///          numeric types, temporal types, YEAR and BIT, this method returns
  ///          the same as max_display_width_in_codepoints(). For character
  ///          types (CHAR, VARCHAR, TEXT etc) the returned value depends on
  ///          max_display_width_in_codepoints() and the character set of this
  ///          column.
  size_t max_display_width_in_bytes() const;

  /// @returns the pack length for this column, which is the number of bytes
  ///          needed to store this column in memory. Note that blob returns
  ///          a length variable + the size of a pointer to an external memory
  ///          location where the actual data is stored. So LONGBLOB would
  ///          return 4 bytes for the length variable + 8 bytes for the pointer
  ///          to the data (12 bytes in total).
  ///  @param dont_override  Don't use pack_length_override even if non-zero
  ///                        Used by multi-valued index, where pack_length
  ///                        and key_length aren't the same.
  size_t pack_length(bool dont_override = false) const;

  /// @returns the key length for this column.
  size_t key_length() const;

  /// @retval true if the maximum column length was given explicitly by the
  ///         user.
  /// @retval false if the user didn't specify any maximum length.
  bool explicit_display_width() const { return m_explicit_display_width; }

  /// Set the maximum display width based on another Create_field.
  void set_max_display_width_from_create_field(
      const Create_field &create_field) {
    m_max_display_width_in_codepoints =
        create_field.max_display_width_in_codepoints();
  }

  dd::Column::enum_hidden_type hidden;

  const char *field_name;
  /**
    Name of column modified by ALTER TABLE's CHANGE/MODIFY COLUMN clauses,
    NULL for columns added.
  */
  const char *change{nullptr};
  const char *after{nullptr};  // Put column after this one
  LEX_CSTRING comment;         // Comment for field

  /**
     The declared default value, if any, otherwise NULL. Note that this member
     is NULL if the default is a function. If the column definition has a
     function declared as the default, the information is found in
     Create_field::auto_flags.

     @see Create_field::auto_flags
  */
  Item *constant_default;
  enum_field_types sql_type;
  uint decimals;
  uint flags{0};
  /**
    Bitmap of flags indicating if field value should be auto-generated
    by default and/or on update, and in which way.

    @sa Field::enum_auto_flags for possible options.
  */
  uchar auto_flags{Field::NONE};
  TYPELIB *interval;  // Which interval to use
                      // Used only for UCS2 intervals
  List<String> interval_list;
  const CHARSET_INFO *charset;
  bool is_explicit_collation{false};  // User explicitly provided charset?
  Field::geometry_type geom_type{Field::GEOM_GEOMETRY};
  Field *field;  // For alter table

  uint offset;

  /**
    Indicate whether column is nullable, zerofill or unsigned.

    Initialized based on flags and other members at prepare_create_field()/
    init_for_tmp_table() stage.
  */
  bool is_nullable{false};
  bool is_zerofill{false};
  bool is_unsigned{false};

  /**
    Indicates that storage engine doesn't support optimized BIT field
    storage.

    @note We also use safe/non-optimized version of BIT field for
          special cases like virtual temporary tables.

    Initialized at mysql_prepare_create_table()/sp_prepare_create_field()/
    init_for_tmp_table() stage.
  */
  bool treat_bit_as_char{false};

  /**
    Row based replication code sometimes needs to create ENUM and SET
    fields with pack length which doesn't correspond to number of
    elements in interval TYPELIB.

    When this member is non-zero ENUM/SET field to be created will use
    its value as pack length instead of one calculated from number
    elements in its interval.

    Initialized at prepare_create_field()/init_for_tmp_table() stage.
  */
  uint pack_length_override{0};

  /// Generated column expression information.
  Value_generator *gcol_info{nullptr};
  /**
    Indication that the field is phycically stored in tables
    rather than just generated on SQL queries.
    As of now, false can only be set for virtual generated columns.
  */
  bool stored_in_db{false};

  /// Holds the expression to be used to generate default values.
  Value_generator *m_default_val_expr{nullptr};
  /// The name of the masking policy to apply on the column when reading from
  /// it. An empty string if there is no masking policy.
  LEX_CSTRING m_masking_policy_name = EMPTY_CSTR;
  std::optional<gis::srid_t> m_srid;

  // Whether the field is actually an array of the field's type;
  bool is_array{false};

  LEX_CSTRING m_engine_attribute = EMPTY_CSTR;
  LEX_CSTRING m_secondary_engine_attribute = EMPTY_CSTR;
  /// Will be converted to m_engine_attribute for persistence
  LEX_CSTRING m_external_format = EMPTY_CSTR;

  Create_field() = default;
  Create_field(Field *field, Field *orig_field);

  /* Used to make a clone of this object for ALTER/CREATE TABLE */
  Create_field *clone(MEM_ROOT *mem_root) const {
    return new (mem_root) Create_field(*this);
  }
  bool is_gcol() const { return gcol_info; }
  bool is_virtual_gcol() const {
    return gcol_info && !gcol_info->get_field_stored();
  }

  /* Init for a tmp table field. To be extended if need be. */
  void init_for_tmp_table(enum_field_types sql_type_arg, uint32 max_length,
                          uint32 decimals, bool is_nullable, bool is_unsigned,
                          uint pack_length_override,
                          const char *field_name = "");

  bool init(THD *thd, const char *field_name, enum_field_types type,
            const char *length, const char *decimals, uint type_modifier,
            Item *default_value, Item *on_update_value,
            const LEX_CSTRING *comment, const char *change,
            List<String> *interval_list, const CHARSET_INFO *cs,
            bool has_explicit_collation, uint uint_geom_type,
            Value_generator *gcol_info, Value_generator *default_val_expr,
            LEX_CSTRING fld_masking_policy, std::optional<gis::srid_t> srid,
            dd::Column::enum_hidden_type hidden, bool is_array = false);

  ha_storage_media field_storage_type() const {
    return (ha_storage_media)((flags >> FIELD_FLAGS_STORAGE_MEDIA) & 3);
  }

  column_format_type column_format() const {
    return (column_format_type)((flags >> FIELD_FLAGS_COLUMN_FORMAT) & 3);
  }

 private:
  /// The maximum display width of this column.
  ///
  /// The "display width" is the number of code points that is needed to print
  /// out the string representation of a value. It can be given by the user
  /// both explicitly and implicitly. If a user creates a table with the columns
  /// "a VARCHAR(3), b INT(3)", both columns are given an explicit display width
  /// of 3 code points. But if a user creates a table with the columns
  /// "a INT, b TINYINT UNSIGNED", the first column has an implicit display
  /// width of 11 (-2147483648 is the longest value for a signed int) and the
  /// second column has an implicit display width of 3 (255 is the longest value
  /// for an unsigned tinyint).
  /// This is related to storage size for some types (VARCHAR, BLOB etc), but
  /// not for all types (an INT is four bytes regardless of the display width).
  ///
  /// A "code point" is basically a numeric value. For instance, ASCII
  /// compromises of 128 code points (0x00 to 0x7F), while unicode contains way
  /// more. In most cases a code point represents a single graphical unit (aka
  /// grapheme), but not always. For instance, É may consists of two code points
  /// where one is the letter E and the other one is the quotation mark above
  /// the letter.
  size_t m_max_display_width_in_codepoints{0};

  /// Whether or not the display width was given explicitly by the user.
  bool m_explicit_display_width{false};
};

/// @returns whether or not this field is a hidden column that represents a
///          functional index.
bool is_field_for_functional_index(const Create_field *create_field);

/**
  @retval true  If this column is hidden either in the storage engine
                or SQL layer. Either way, it is completely hidden from
                the user.
  @retval false Otherwise.
*/
bool is_hidden_by_system(const Create_field *create_field);

/**
  @retval true  If this column is hidden by the user.
  @retval false otherwise.
*/
bool is_hidden_by_user(const Create_field *create_field);
#endif