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mariadb-dev
mariadb/sql/sql_cursor.h
Alexander Barkov 90f8178f33 MDEV-10152 Add support for TYPE .. IS REF CURSOR 
Adding support for the strict cursor data types:

Example 1a:
  TYPE rec0_t IS RECORD (a INT, VARCHAR(10));
  TYPE cur0_t IS REF CURSOR RETURN rec0_t;

Example 1b:
  TYPE rec0_t IS RECORD (a t1.a%TYPE, b t1.b%TYPE);
  TYPE cur0_t IS REF CURSOR RETURN rec0_t;

Example 1c:
  TYPE rec0_t IS RECORD (a INT, VARCHAR(10));
  r0 rec0_t;
  TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;

Example 1d:
  TYPE rec0_t IS RECORD (a t1.a%TYPE, b t1.b%TYPE);
  r0 rec0_t;
  TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;

Example2a:
  TYPE cur0_t IS REF CURSOR RETURN t1%ROWTYPE; -- t1 is a table

Example 2b:
  r0 t1%ROWTYPE;
  TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;

Example3a:
  CURSOR cursor_sample IS SELECT a,b FROM t1;
  TYPE cur0_t IS REF CURSOR RETURN cursor_sample%ROWTYPE;

Example3b:
  CURSOR cursor_sample IS SELECT a,b FROM t1;
  r0 cursor_sample%ROWTYPE;
  TYPE cur0_t IS REF CURSOR RETURN r0%TYPE;

If a cursor variable is declared with a RETURN clause then:
1. At OPEN type the data type of the SELECT list row is compared
  for compatibility with the cursor RETURN data type.
  The SELECT list row must be assignable to the RETURN type row.
  If case if assignability is not meet, an error is raised
  Assignability means:
  - The arity of the SELECT list must be equal to the arity
    of the RETURN clause
  - Every n-th field of the SELECT list must be assignable to the
    n-th field of the RETURN Clause

2. At FETCH time, the data is fetched in two steps:
  a. On the first step the data is fetched into a virtual table
     with the row type described in the RETURN clause
  b. On the second step the data is copied from the virtual table
     to the target fetch list. Data type conversion can happen
     on this step.

Change details:

Adding new methods:
- sp_cursor::check_assignability_to
- Virtual_tmp_table::check_assignability_from
- Virtual_tmp_table::sp_set_from_select_list
- Virtual_tmp_table::sp_save_in_vtable
- Virtual_tmp_table::sp_save_in_target_list
- LEX::check_ref_cursor_components
- LEX::make_sp_instr_copy_struct_for_last_context_variables
- LEX::declare_type_ref_cursor
- sp_cursor::Select_fetch_into_spvars::send_data_with_return_type

Adding new members:
- sp_instr_copen_by_ref::m_cursor_name
- Select_fetch_into_spvars::m_return_type
- Select_materialize::m_cursor_name
- Select_materialize::m_return_type

Adding new virtual methods:
- Item::resolve_spvar_cursor_rowtype
- Type_handler::Spvar_definition_resolve_type_refs
- Server_side_cursor::check_assignability_to
- Overriding Select_materialize::prepare to raise an error when the cursor
  returned data type is not compatible with the RETURN clause

Making these methods virtual:
- Field::check_assignability_from

Adding new classes:
- sp_type_def_ref
- RowTypeBuffer

Adding new constructors to:
- Spvar_definition

Adding new helper methods (e.g. to reuse the code)
- Field::store_field_maybe_null
- ChanBuffer::append_ulonglong
- sp_pcontext::set_type_for_last_context_variables

Minor changes:
- Making TABLE::export_structure const
- Overriding Item_splocal::type_extra_attributes. It was forgotten in earlier changes.

Adding new error messages
- ER_CANNOT_CAST_ON_IDENT1_ASSIGNMENT_FOR_OPERATION
- ER_CANNOT_CAST_ON_IDENT2_ASSIGNMENT_FOR_OPERATION
2026-04-06 15:16:38 +04:00

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/* Copyright (c) 2005, 2011, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
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 for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
#ifndef _sql_cursor_h_
#define _sql_cursor_h_
#include "sql_class.h" /* Query_arena */
#include "sql_select.h"
class JOIN;
/**
@file
Declarations for implementation of server side cursors. Only
read-only non-scrollable cursors are currently implemented.
*/
/**
Server_side_cursor -- an interface for materialized
implementation of cursors. All cursors are self-contained
(created in their own memory root). For that reason they must
be deleted only using a pointer to Server_side_cursor, not to
its base class.
*/
class Server_side_cursor: protected Query_arena
{
protected:
/** Row destination used for fetch */
select_result *result;
public:
Server_side_cursor(MEM_ROOT *mem_root_arg, select_result *result_arg)
:Query_arena(mem_root_arg, STMT_INITIALIZED), result(result_arg)
{}
virtual bool is_open() const= 0;
virtual int open(JOIN *top_level_join)= 0;
virtual void fetch(ulong num_rows)= 0;
virtual void close()= 0;
virtual bool export_structure(THD *thd, Row_definition_list *defs) const
{
DBUG_ASSERT(0);
return true;
}
virtual bool check_assignability_to(const Virtual_tmp_table *table,
const char *spvar_name,
const char *op) const
{
DBUG_ASSERT(0);
return false;
}
virtual ~Server_side_cursor();
static void *operator new(size_t size, MEM_ROOT *mem_root)
{ return alloc_root(mem_root, size); }
static void operator delete(void *ptr, size_t size);
static void operator delete(void *, MEM_ROOT *){}
};
/**
Materialized_cursor -- an insensitive materialized server-side
cursor. The result set of this cursor is saved in a temporary
table at open. The cursor itself is simply an interface for the
handler of the temporary table.
*/
class Materialized_cursor: public Server_side_cursor
{
MEM_ROOT main_mem_root;
/* A fake unit to supply to select_send when fetching */
SELECT_LEX_UNIT fake_unit;
TABLE *table;
List<Item> item_list;
ulong fetch_limit;
ulong fetch_count;
bool is_rnd_inited;
public:
Materialized_cursor(select_result *result, TABLE *table);
int send_result_set_metadata(THD *thd, List<Item> &send_result_set_metadata);
bool is_open() const override { return table != 0; }
int open(JOIN *join __attribute__((unused))) override;
void fetch(ulong num_rows) override;
void close() override;
bool export_structure(THD *thd, Row_definition_list *defs) const override
{
return table->export_structure(thd, defs);
}
bool check_assignability_to(const Virtual_tmp_table *table,
const char *spvar_name,
const char *op) const override
{
return table->check_assignability_from(item_list, spvar_name, op);
}
~Materialized_cursor() override;
void on_table_fill_finished();
};
/**
Select_materialize -- a mediator between a cursor query and the
protocol. In case we were not able to open a non-materialzed
cursor, it creates an internal temporary HEAP table, and insert
all rows into it. When the table reaches max_heap_table_size,
it's converted to a MyISAM table. Later this table is used to
create a Materialized_cursor.
*/
class Select_materialize: public select_unit
{
select_result *result; /**< the result object of the caller (PS or SP) */
const Lex_ident_column &m_cursor_name;
const Virtual_tmp_table *m_return_type;
public:
Materialized_cursor *materialized_cursor;
Select_materialize(THD *thd_arg, select_result *result_arg,
const Lex_ident_column &cursor_name,
const Virtual_tmp_table *return_type):
select_unit(thd_arg), result(result_arg),
m_cursor_name(cursor_name),
m_return_type(return_type),
materialized_cursor(0) {}
int prepare(List<Item> &list, SELECT_LEX_UNIT *u) override;
bool send_result_set_metadata(List<Item> &list, uint flags) override;
bool send_eof() override { return false; }
bool view_structure_only() const override
{
return result->view_structure_only();
}
};
int mysql_open_cursor(THD *thd, select_result *result,
Server_side_cursor **res,
const Lex_ident_column &cursor_name,
const Virtual_tmp_table *return_type);
#endif /* _sql_cusor_h_ */
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