This task is intended to simplify the work for CREATE PACKAGE (see MDEV-10591), as well as to fix minor known problems in the underlying parser grammar.

There are a few difficulties in the grammar for CREATE for VIEW, TRIGGER, EVENT, PROCEDURE, FUNCTION.

• The grammar for the mentioned objects is implemented with help of the rule view_or_trigger_or_sp_or_event. The grammar for all other object types is implemented directly in the create: rule. This makes the grammar non-symmetric for various object types, which is hard to read and understand.

• We'll add CREATE PACKAGE soon. It will require the DEFINER clause. In the current grammar, it will have to go to view_or_trigger_or_sp_or_event again, and make the things even more complex.

• LEX::create_view_mode, LEX::create_view_algorithm, LEX::create_view_suid are initialized for all objects described in view_or_trigger_or_sp_or_event. For non-VIEW objects this initialization is redundant.

  | create_or_replace

  {

  Lex->create_info.set($1);

  Lex->create_view_mode= ($1.or_replace() ? VIEW_CREATE_OR_REPLACE :

  VIEW_CREATE_NEW);

  Lex->create_view_algorithm= DTYPE_ALGORITHM_UNDEFINED;

  Lex->create_view_suid= TRUE;

  }

  view_or_trigger_or_sp_or_event { }

• The grammar erroneously accepts these weird query:

  ALTER VIEW IF NOT EXISTS v1 AS SELECT 1;

  It's really senseless to ALTER something that NOT EXISTS.
  The IF NOT EXISTS clause is accepted because both CREATE VIEW and ALTER VIEW grammar reuses the view_tail rule.

Under terms of this task we'll do the following:

• For stricter data type control: introduce a new enum instead of pre-processor constants:

enum enum_view_suid

{

  VIEW_SUID_INVOKER= 0,

  VIEW_SUID_DEFINER= 1,

  VIEW_SUID_DEFAULT= 2

};

• Introduce a new class:

class Create_view_info: public Sql_alloc

{

public:

  LEX_CSTRING select;              // The SELECT statement of CREATE VIEW

  enum enum_view_create_mode mode;

  uint16 algorithm;

  uint8 check;

  enum enum_view_suid suid;

  Create_view_info(enum_view_create_mode mode_arg,

                   uint16 algorithm_arg,

                   enum_view_suid suid_arg)

   :select(null_clex_str),

    mode(mode_arg),

    algorithm(algorithm_arg),

    check(VIEW_CHECK_NONE),  

    suid(suid_arg)

  { }

}; 

• Remove the same members from LEX and add a pointer to Create_view_info instead. Create_view_info will be allocated on THD memory root only for CREATE VIEW or ALTER VIEW queries.

• Reduce the amount of duplicate C++ code used in .yy files by adding new methods in LEX:

  bool add_alter_view(THD *thd, uint16 algorithm, enum_view_suid suid,

                      Table_ident *table_ident);

  bool add_create_view(THD *thd, DDL_options_st ddl,

                       uint16 algorithm, enum_view_suid suid,

                       Table_ident *table_ident);

• In sql_yacc.yy: remove grammar rules view_or_trigger_or_sp_or_event, definer_tail, no_definer_tail, view_tail

• In sql_yacc.yy: add new grammar branches directly into the create: rules, for VIEW, TRIGGER, PROCEDURE, FUNCTION, EVENT.
  Note, when we add the CREATE PACKAGE statement later (see MDEV-10591), it will also be added directly to create:, together with its optional DEFINER clause.

• In sql_yacc.yy: fix the rules view_algorithm, view_suid, view_check_options to return values in $$, instead of setting thd->lex members directly. This is needed to pass these values to the new methods LEX::add_alter_view() and LEX::add_create_view().

• Do corresponding changes in sql_yacc_ora.yy.