[#MDEV-8095] Split Create

Create_field is a big class and some of its parts are not really used in many contexts.
Before adding pluggable data types under terms of ~~MDEV-4912~~, it would be nice to clean-up use of Create_field.

Under terms of this task we will:

1. Move members of Create_field that are needed only at ALTER time into a separate class Alter_column_specification:

class Alter_column_specification

public:

  const char *change;                   // If done with alter table

  const char *after;                    // Put column after this one

  Field *field;                         // For alter table

  TYPELIB *save_interval;               // Temporary copy for the above

                                        // Used only for UCS2 intervals

  uint offset;

  uint8 interval_id;                    // For rea_create_table

  bool create_if_not_exists;            // Used in ALTER TABLE IF NOT EXISTS

};

2. Move the rest of Create_field members (except field_name) into a separate class Column_specification.

class Column_specification

public:

  LEX_STRING comment;

  Item *def, *on_update;

  enum  enum_field_types sql_type;

  ulonglong length;

  uint32 char_length;

  uint  decimals, flags, pack_length, key_length;

  Field::utype unireg_check;

  TYPELIB *interval;

  List<String> interval_list;

  CHARSET_INFO *charset;

  uint32 srid;

  Field::geometry_type geom_type;

  engine_option_value *option_list;

  ha_field_option_struct *option_struct;

  uint  pack_flag;

  Virtual_column_info *vcol_info;

  bool stored_in_db;

};

3. Derive Create_field from Column_specification and Alter_column_specification:

class Create_field: public Column_specification,

                    public Alter_column_specification,

                    public Sql_alloc

public:

  LEX_CSTRING field_name;

};

Note, Create_field::field_name will be changed from "const char *" to LEX_CSTRING
under terms of ~~MDEV-8092~~.

4. Change data type of sp_variable::field_def and sp_head::m_return_field_def
from Create_field to Column_specification. These classes need neither the
Alter_column_specification nor the "field_name" parts of Create_field.

[MDEV-8095] Split Create_field Created: 2015-05-04 Updated: 2021-05-11
Status:	Open
Project:	MariaDB Server
Component/s:	None
Fix Version/s:	None

[MDEV-8095] Split Create_field Created: 2015-05-04 Updated: 2021-05-11