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MWL#17: Table elimination
- Do not show eliminated tables in the output of EXPLAIN EXTENDED
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parent
fd485ad988
commit
402e58cf78
5 changed files with 45 additions and 16 deletions
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@ -10,6 +10,11 @@ as select a, a as b from t1 where a in (1,3);
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explain select t1.a from t1 left join t2 on t2.a=t1.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4
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explain extended select t1.a from t1 left join t2 on t2.a=t1.a;
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id select_type table type possible_keys key key_len ref rows filtered Extra
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4 100.00
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Warnings:
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Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where 1
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select t1.a from t1 left join t2 on t2.a=t1.a;
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a
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0
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@ -45,14 +50,16 @@ explain select t1.a from t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4
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# Elimination when done within an outer join nest:
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explain
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explain extended
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select t0.*
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from
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t0 left join (t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and
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t3.a=t1.a) on t0.a=t1.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 4
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4
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id select_type table type possible_keys key key_len ref rows filtered Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 4 100.00
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1 SIMPLE t1 ALL NULL NULL NULL NULL 4 100.00
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Warnings:
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Note 1003 select `test`.`t0`.`a` AS `a` from `test`.`t0` left join (`test`.`t1`) on((`test`.`t0`.`a` = `test`.`t1`.`a`)) where 1
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# Elimination with aggregate functions
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explain select count(*) from t1 left join t2 on t2.a=t1.a;
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id select_type table type possible_keys key key_len ref rows Extra
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@ -17,6 +17,7 @@ create table t3 (a int primary key, b int)
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--echo # This will be eliminated:
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explain select t1.a from t1 left join t2 on t2.a=t1.a;
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explain extended select t1.a from t1 left join t2 on t2.a=t1.a;
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select t1.a from t1 left join t2 on t2.a=t1.a;
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@ -39,7 +40,7 @@ explain select t1.a from t1 left join (t2 join t3) on t2.a=t1.a and t3.a=t1.a;
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explain select t1.a from t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and t3.a=t1.a;
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--echo # Elimination when done within an outer join nest:
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explain
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explain extended
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select t0.*
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from
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t0 left join (t1 left join (t2 join t3 on t2.b=t3.b) on t2.a=t1.a and
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@ -2386,6 +2386,10 @@ mysql_select(THD *thd, Item ***rref_pointer_array,
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}
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else
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{
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// psergey{
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if (select_options & SELECT_DESCRIBE)
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free_join= 0;
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// }psergey
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if (!(join= new JOIN(thd, fields, select_options, result)))
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DBUG_RETURN(TRUE);
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thd_proc_info(thd, "init");
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@ -2523,7 +2527,7 @@ static void mark_table_as_eliminated(JOIN *join, TABLE *table, uint *const_tbl_c
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{
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DBUG_PRINT("info", ("Eliminated table %s", table->alias));
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tab->type= JT_CONST;
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tab->eliminated= TRUE;
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join->eliminated_tables |= table->map;
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*const_tables |= table->map;
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join->const_table_map|= table->map;
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set_position(join, (*const_tbl_count)++, tab, (KEYUSE*)0);
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@ -2726,6 +2730,10 @@ static void eliminate_tables(JOIN *join, uint *const_tbl_count, table_map *const
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Item *item;
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table_map used_tables;
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DBUG_ENTER("eliminate_tables");
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join->eliminated_tables= 0;
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/* MWL#17 is only about outer join elimination, so: */
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if (!join->outer_join)
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DBUG_VOID_RETURN;
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@ -6060,6 +6068,7 @@ JOIN::make_simple_join(JOIN *parent, TABLE *tmp_table)
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tables= 1;
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const_tables= 0;
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const_table_map= 0;
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eliminated_tables= 0;
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tmp_table_param.field_count= tmp_table_param.sum_func_count=
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tmp_table_param.func_count= 0;
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tmp_table_param.copy_field= tmp_table_param.copy_field_end=0;
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@ -16509,7 +16518,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
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quick_type= -1;
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//psergey-todo:
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if (tab->eliminated)
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if (table->map & join->eliminated_tables)
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{
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used_tables|=table->map;
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continue;
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@ -16912,6 +16921,7 @@ bool mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
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*/
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static void print_join(THD *thd,
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table_map eliminated_tables,
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String *str,
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List<TABLE_LIST> *tables,
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enum_query_type query_type)
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@ -16927,12 +16937,22 @@ static void print_join(THD *thd,
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*t= ti++;
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DBUG_ASSERT(tables->elements >= 1);
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(*table)->print(thd, str, query_type);
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//pserey:TODO check!
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(*table)->print(thd, eliminated_tables, str, query_type);
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TABLE_LIST **end= table + tables->elements;
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for (TABLE_LIST **tbl= table + 1; tbl < end; tbl++)
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{
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TABLE_LIST *curr= *tbl;
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// psergey-todo-todo:
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// base table: check
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if (curr->table && (curr->table->map & eliminated_tables) ||
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curr->nested_join && !(curr->nested_join->used_tables &
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~eliminated_tables))
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{
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continue;
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}
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if (curr->outer_join)
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{
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/* MySQL converts right to left joins */
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@ -16942,7 +16962,7 @@ static void print_join(THD *thd,
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str->append(STRING_WITH_LEN(" straight_join "));
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else
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str->append(STRING_WITH_LEN(" join "));
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curr->print(thd, str, query_type);
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curr->print(thd, eliminated_tables, str, query_type);
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if (curr->on_expr)
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{
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str->append(STRING_WITH_LEN(" on("));
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@ -16996,12 +17016,13 @@ Index_hint::print(THD *thd, String *str)
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@param str string where table should be printed
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*/
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void TABLE_LIST::print(THD *thd, String *str, enum_query_type query_type)
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void TABLE_LIST::print(THD *thd, table_map eliminated_tables, String *str,
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enum_query_type query_type)
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{
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if (nested_join)
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{
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str->append('(');
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print_join(thd, str, &nested_join->join_list, query_type);
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print_join(thd, eliminated_tables, str, &nested_join->join_list, query_type);
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str->append(')');
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}
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else
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@ -17143,7 +17164,7 @@ void st_select_lex::print(THD *thd, String *str, enum_query_type query_type)
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{
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str->append(STRING_WITH_LEN(" from "));
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/* go through join tree */
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print_join(thd, str, &top_join_list, query_type);
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print_join(thd, join->eliminated_tables, str, &top_join_list, query_type);
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}
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else if (where)
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{
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@ -211,9 +211,6 @@ typedef struct st_join_table {
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/** Bitmap of nested joins this table is part of */
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nested_join_map embedding_map;
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//psergey-todo: more justified place
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bool eliminated;
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void cleanup();
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inline bool is_using_loose_index_scan()
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{
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@ -289,6 +286,8 @@ public:
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*/
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bool resume_nested_loop;
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table_map const_table_map,found_const_table_map;
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table_map eliminated_tables;
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/*
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Bitmap of all inner tables from outer joins
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*/
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@ -1366,7 +1366,8 @@ struct TABLE_LIST
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return (derived || view || schema_table || (create && !table->db_stat) ||
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!table);
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}
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void print(THD *thd, String *str, enum_query_type query_type);
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void print(THD *thd, table_map eliminated_tables, String *str,
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enum_query_type query_type);
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bool check_single_table(TABLE_LIST **table, table_map map,
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TABLE_LIST *view);
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bool set_insert_values(MEM_ROOT *mem_root);
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