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Allow queries of multiple SELECTs combined together with UNIONs/EXCEPTs/INTERSECTs to be pushed down to foreign engines. If the foreign engine provides an interface method "create_unit" and the UNIT is a top-level unit of the SQL query then the server tries to push the whole SELECT_LEX_UNIT down to the engine for execution. The engine should perform necessary checks and if they succeed, execute the query. If the engine is unable to execute the whole unit, then another attempt is made to push down SELECTs composing the unit separately using the "create_select" interface method. In this case the results of separate SELECTs are combined at the server side thus composing the final result
112 lines
3.2 KiB
Objective-C
112 lines
3.2 KiB
Objective-C
/*
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Copyright (c) 2018, 2019 MariaDB
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
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#ifndef SELECT_HANDLER_INCLUDED
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#define SELECT_HANDLER_INCLUDED
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#include "mariadb.h"
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#include "sql_priv.h"
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/**
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@class select_handler
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This interface class is to be used for execution of select queries
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by foreign engines
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*/
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class select_handler
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{
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public:
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// Constructor for a single SELECT_LEX (not a part of a unit)
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select_handler(THD *thd_arg, handlerton *ht_arg, SELECT_LEX *sel_lex);
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// Constructor for a unit (UNION/EXCEPT/INTERSECT)
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select_handler(THD *thd_arg, handlerton *ht_arg, SELECT_LEX_UNIT *sel_unit);
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/*
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Constructor for a SELECT_LEX which is a part of a unit
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(partial pushdown). Both SELECT_LEX and SELECT_LEX_UNIT are passed
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*/
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select_handler(THD *thd_arg, handlerton *ht_arg, SELECT_LEX *sel_lex,
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SELECT_LEX_UNIT *sel_unit);
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virtual ~select_handler();
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int execute();
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virtual bool prepare();
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/*
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Select_handler processes one of
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- single SELECT
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- whole unit (multiple SELECTs combined with UNION/EXCEPT/INTERSECT)
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- single SELECT that is part of a unit (partial pushdown)
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In the case of single SELECT select_lex is initialized and lex_unit==NULL,
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in the case of whole UNIT select_lex == NULL and lex_unit is initialized,
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in the case of partial pushdown both select_lex and lex_unit
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are initialized
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*/
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SELECT_LEX *select_lex; // Single select to be executed
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SELECT_LEX_UNIT *lex_unit; // Unit to be executed
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/*
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Temporary table where all results should be stored in record[0]
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The table has a field for every item from the select_lex::item_list.
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The table is actually never filled. Only its record buffer is used.
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*/
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TABLE *table;
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protected:
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/*
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Functions to scan the select result set.
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All these returns 0 if ok, error code in case of error.
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*/
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/* Initialize the process of producing rows of result set */
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virtual int init_scan() = 0;
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/*
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Put the next produced row of the result set in table->record[0]
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and return 0. Return HA_ERR_END_OF_FILE if there are no more rows,
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return other error number in case of fatal error.
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*/
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virtual int next_row() = 0;
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/* Finish scanning */
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virtual int end_scan() = 0;
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/* Report errors */
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virtual void print_error(int error, myf errflag);
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bool send_result_set_metadata();
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bool send_data();
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bool send_eof();
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TABLE *create_tmp_table(THD *thd);
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THD *thd;
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handlerton *ht;
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select_result *result; // Object receiving the retrieved data
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List<Item> result_columns;
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bool is_analyze;
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};
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#endif /* SELECT_HANDLER_INCLUDED */
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