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	|  f11504af51 This patch adds support for SYS_REFCURSOR (a weakly typed cursor)
for both sql_mode=ORACLE and sql_mode=DEFAULT.
Works as a regular stored routine variable, parameter and return value:
- can be passed as an IN parameter to stored functions and procedures
- can be passed as an INOUT and OUT parameter to stored procedures
- can be returned from a stored function
Note, strongly typed REF CURSOR will be added separately.
Note, to maintain dependencies easier, some parts of sql_class.h
and item.h were moved to new header files:
- select_results.h:
  class select_result_sink
  class select_result
  class select_result_interceptor
- sp_cursor.h:
  class sp_cursor_statistics
  class sp_cursor
- sp_rcontext_handler.h
  class Sp_rcontext_handler and its descendants
The implementation consists of the following parts:
- A new class sp_cursor_array deriving from Dynamic_array
- A new class Statement_rcontext which contains data shared
  between sub-statements of a compound statement.
  It has a member m_statement_cursors of the sp_cursor_array data type,
  as well as open cursor counter. THD inherits from Statement_rcontext.
- A new data type handler Type_handler_sys_refcursor in plugins/type_cursor/
  It is designed to store uint16 references -
  positions of the cursor in THD::m_statement_cursors.
- Type_handler_sys_refcursor suppresses some derived numeric features.
  When a SYS_REFCURSOR variable is used as an integer an error is raised.
- A new abstract class sp_instr_fetch_cursor. It's needed to share
  the common code between "OPEN cur" (for static cursors) and
  "OPER cur FOR stmt" (for SYS_REFCURSORs).
- New sp_instr classes:
  * sp_instr_copen_by_ref      - OPEN sys_ref_curor FOR stmt;
  * sp_instr_cfetch_by_ref     - FETCH sys_ref_cursor INTO targets;
  * sp_instr_cclose_by_ref     - CLOSE sys_ref_cursor;
  * sp_instr_destruct_variable - to destruct SYS_REFCURSOR variables when
                                 the execution goes out of the BEGIN..END block
                                 where SYS_REFCURSOR variables are declared.
- New methods in LEX:
  * sp_open_cursor_for_stmt   - handles "OPEN sys_ref_cursor FOR stmt".
  * sp_add_instr_fetch_cursor - "FETCH cur INTO targets" for both
                                static cursors and SYS_REFCURSORs.
  * sp_close - handles "CLOSE cur" both for static cursors and SYS_REFCURSORs.
- Changes in cursor functions to handle both static cursors and SYS_REFCURSORs:
  * Item_func_cursor_isopen
  * Item_func_cursor_found
  * Item_func_cursor_notfound
  * Item_func_cursor_rowcount
- A new system variable @@max_open_cursors - to limit the number
  of cursors (static and SYS_REFCURSORs) opened at the same time.
  Its allowed range is [0-65536], with 50 by default.
- A new virtual method Type_handler::can_return_bool() telling
  if calling item->val_bool() is allowed for Items of this data type,
  or if otherwise the "Illegal parameter for operation" error should be raised
  at fix_fields() time.
- New methods in Sp_rcontext_handler:
  * get_cursor()
  * get_cursor_by_ref()
- A new class Sp_rcontext_handler_statement to handle top level statement
  wide cursors which are shared by all substatements.
- A new virtual method expr_event_handler() in classes Item and Field.
  It's needed to close (and make available for a new OPEN)
  unused THD::m_statement_cursors elements which do not have any references
  any more. It can happen in various moments in time, e.g.
  * after evaluation parameters of an SQL routine
  * after assigning a cursor expression into a SYS_REFCURSOR variable
  * when leaving a BEGIN..END block with SYS_REFCURSOR variables
  * after setting OUT/INOUT routine actual parameters from formal
    parameters. | ||
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| audit_null | ||
| auth_dialog | ||
| auth_ed25519 | ||
| auth_examples | ||
| auth_gssapi | ||
| auth_pam | ||
| auth_parsec | ||
| auth_pipe | ||
| auth_socket | ||
| aws_key_management | ||
| cracklib_password_check | ||
| daemon_example | ||
| debug_key_management | ||
| disks | ||
| example_key_management | ||
| feedback | ||
| file_key_management | ||
| fulltext | ||
| func_test | ||
| handler_socket | ||
| hashicorp_key_management | ||
| locale_info | ||
| metadata_lock_info | ||
| password_reuse_check | ||
| provider_bzip2 | ||
| provider_lz4 | ||
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| provider_lzo | ||
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| qc_info | ||
| query_response_time | ||
| server_audit | ||
| simple_password_check | ||
| sql_errlog | ||
| test_sql_service | ||
| type_cursor | ||
| type_geom | ||
| type_inet | ||
| type_mysql_json | ||
| type_mysql_timestamp | ||
| type_test | ||
| type_uuid | ||
| user_variables | ||
| userstat | ||
| versioning | ||
| win_auth_client | ||
| wsrep_info | ||