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Fixed LP BUG#641203: Query returns rows where no result is expected (impossible WHERE)
The cause for the bug was two-fold: 1. Incorrect detection of whether a table is the first one in a query plan - "used_table & 1" actually checks if used_table is table with number "1". 2. Missing logic to delay the evaluation of (expensive) constant conditions during the execution phase. The fix adds/changes: The patch: - removes incorrect treatment of expensive predicates from make_cond_for_table, and lets the caller decide when to evaluate expensive predicates. - saves expensive constant conditions in JOIN::exec_const_cond, which is evaluated once in the beginning of JOIN::exec.
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4 changed files with 90 additions and 33 deletions
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@ -397,3 +397,42 @@ pk
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# Restore old value for Index condition pushdown
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SET SESSION engine_condition_pushdown=@old_icp;
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DROP TABLE t1,t2;
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#
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# LP BUG#641203 Query returns rows where no result is expected (impossible WHERE)
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#
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CREATE TABLE t1 (c1 varchar(1) DEFAULT NULL);
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CREATE TABLE t2 (c1 varchar(1) DEFAULT NULL);
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INSERT INTO t2 VALUES ('k'), ('d');
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CREATE TABLE t3 (c1 varchar(1) DEFAULT NULL);
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INSERT INTO t3 VALUES ('a'), ('b'), ('c');
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CREATE TABLE t4 (c1 varchar(1) primary key);
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INSERT INTO t4 VALUES ('k'), ('d');
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EXPLAIN
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SELECT * FROM t1 RIGHT JOIN t2 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
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SELECT * FROM t1 RIGHT JOIN t2 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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c1 c1
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EXPLAIN
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SELECT * FROM t2 LEFT JOIN t1 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
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SELECT * FROM t2 LEFT JOIN t1 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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c1 c1
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EXPLAIN
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SELECT * FROM (t2 LEFT JOIN t1 ON t1.c1) LEFT JOIN t3 on t3.c1 WHERE 's' IN (SELECT c1 FROM t2);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
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SELECT * FROM (t2 LEFT JOIN t1 ON t1.c1) LEFT JOIN t3 on t3.c1 WHERE 's' IN (SELECT c1 FROM t2);
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c1 c1 c1
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EXPLAIN
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SELECT * FROM t4 LEFT JOIN t2 ON t4.c1 WHERE 's' IN (SELECT c1 FROM t2);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 DEPENDENT SUBQUERY t2 ALL NULL NULL NULL NULL 2 Using where
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SELECT * FROM t4 LEFT JOIN t2 ON t4.c1 WHERE 's' IN (SELECT c1 FROM t2);
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c1 c1
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drop table t1, t2, t3, t4;
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@ -370,3 +370,29 @@ WHERE
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SET SESSION engine_condition_pushdown=@old_icp;
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DROP TABLE t1,t2;
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--echo #
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--echo # LP BUG#641203 Query returns rows where no result is expected (impossible WHERE)
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--echo #
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CREATE TABLE t1 (c1 varchar(1) DEFAULT NULL);
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CREATE TABLE t2 (c1 varchar(1) DEFAULT NULL);
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INSERT INTO t2 VALUES ('k'), ('d');
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CREATE TABLE t3 (c1 varchar(1) DEFAULT NULL);
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INSERT INTO t3 VALUES ('a'), ('b'), ('c');
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CREATE TABLE t4 (c1 varchar(1) primary key);
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INSERT INTO t4 VALUES ('k'), ('d');
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EXPLAIN
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SELECT * FROM t1 RIGHT JOIN t2 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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SELECT * FROM t1 RIGHT JOIN t2 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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EXPLAIN
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SELECT * FROM t2 LEFT JOIN t1 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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SELECT * FROM t2 LEFT JOIN t1 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
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EXPLAIN
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SELECT * FROM (t2 LEFT JOIN t1 ON t1.c1) LEFT JOIN t3 on t3.c1 WHERE 's' IN (SELECT c1 FROM t2);
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SELECT * FROM (t2 LEFT JOIN t1 ON t1.c1) LEFT JOIN t3 on t3.c1 WHERE 's' IN (SELECT c1 FROM t2);
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EXPLAIN
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SELECT * FROM t4 LEFT JOIN t2 ON t4.c1 WHERE 's' IN (SELECT c1 FROM t2);
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SELECT * FROM t4 LEFT JOIN t2 ON t4.c1 WHERE 's' IN (SELECT c1 FROM t2);
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drop table t1, t2, t3, t4;
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@ -1821,6 +1821,9 @@ JOIN::exec()
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if (tables)
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thd->limit_found_rows= 0;
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if (exec_const_cond && !exec_const_cond->val_int())
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zero_result_cause= "Impossible WHERE noticed after reading const tables";
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if (zero_result_cause)
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{
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(void) return_zero_rows(this, result, select_lex->leaf_tables,
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@ -6626,11 +6629,12 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
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there inside the triggers.
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*/
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{ // Check const tables
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COND *const_cond=
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join->exec_const_cond=
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make_cond_for_table(cond,
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join->const_table_map,
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(table_map) 0, TRUE);
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DBUG_EXECUTE("where",print_where(const_cond,"constants", QT_ORDINARY););
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(table_map) 0, FALSE);
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DBUG_EXECUTE("where",print_where(join->exec_const_cond, "constants",
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QT_ORDINARY););
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for (JOIN_TAB *tab= join->join_tab+join->const_tables;
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tab < join->join_tab+join->tables ; tab++)
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{
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@ -6639,7 +6643,7 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
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JOIN_TAB *cond_tab= tab->first_inner;
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COND *tmp= make_cond_for_table(*tab->on_expr_ref,
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join->const_table_map,
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( table_map) 0, FALSE);
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(table_map) 0, FALSE);
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if (!tmp)
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continue;
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tmp= new Item_func_trig_cond(tmp, &cond_tab->not_null_compl);
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@ -6655,10 +6659,13 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
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cond_tab->select_cond->quick_fix_field();
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}
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}
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if (const_cond && !const_cond->val_int())
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if (join->exec_const_cond && !join->exec_const_cond->is_expensive() &&
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!join->exec_const_cond->val_int())
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{
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DBUG_PRINT("info",("Found impossible WHERE condition"));
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DBUG_RETURN(1); // Impossible const condition
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DBUG_PRINT("info",("Found impossible WHERE condition"));
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join->exec_const_cond= NULL;
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DBUG_RETURN(1); // Impossible const condition
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}
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}
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}
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@ -14622,7 +14629,6 @@ bool test_if_ref(Item *root_cond, Item_field *left_item,Item *right_item)
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}
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/*
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Extract a condition that can be checked after reading given table
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@ -14658,32 +14664,17 @@ bool test_if_ref(Item *root_cond, Item_field *left_item,Item *right_item)
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static Item *
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make_cond_for_table(Item *cond, table_map tables, table_map used_table,
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bool exclude_expensive_cond)
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bool exclude_expensive_cond __attribute__((unused)))
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{
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return make_cond_for_table_from_pred(cond, cond, tables, used_table,
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exclude_expensive_cond);
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}
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static Item *
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make_cond_for_table_from_pred(Item *root_cond, Item *cond,
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table_map tables, table_map used_table,
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bool exclude_expensive_cond)
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bool exclude_expensive_cond __attribute__((unused)))
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{
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if (used_table && !(cond->used_tables() & used_table) &&
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/*
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Exclude constant conditions not checked at optimization time if
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the table we are pushing conditions to is the first one.
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As a result, such conditions are not considered as already checked
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and will be checked at execution time, attached to the first table.
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psergey: TODO: "used_table & 1" doesn't make sense in nearly any
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context. Look at setup_table_map(), table bits reflect the order
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the tables were encountered by the parser. Check what we should
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replace this condition with.
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*/
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!((used_table & 1) && cond->is_expensive()))
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return (COND*) 0; // Already checked
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if (cond->type() == Item::COND_ITEM)
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{
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if (((Item_cond*) cond)->functype() == Item_func::COND_AND_FUNC)
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@ -14751,12 +14742,7 @@ make_cond_for_table_from_pred(Item *root_cond, Item *cond,
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table_count times, we mark each item that we have examined with the result
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of the test
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*/
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if (cond->marker == 3 || (cond->used_tables() & ~tables) ||
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/*
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When extracting constant conditions, treat expensive conditions as
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non-constant, so that they are not evaluated at optimization time.
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*/
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(!used_table && exclude_expensive_cond && cond->is_expensive()))
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if (cond->marker == 3 || (cond->used_tables() & ~tables))
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return (COND*) 0; // Can't check this yet
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if (cond->marker == 2 || cond->eq_cmp_result() == Item::COND_OK)
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return cond; // Not boolean op
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@ -14784,7 +14770,6 @@ make_cond_for_table_from_pred(Item *root_cond, Item *cond,
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}
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static COND *
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make_cond_after_sjm(Item *root_cond, Item *cond, table_map tables,
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table_map sjm_tables)
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@ -1593,6 +1593,12 @@ public:
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List<TABLE_LIST> *join_list; ///< list of joined tables in reverse order
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COND_EQUAL *cond_equal;
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COND_EQUAL *having_equal;
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/*
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Constant codition computed during optimization, but evaluated during
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join execution. Typically expensive conditions that should not be
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evaluated at optimization time.
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*/
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Item *exec_const_cond;
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SQL_SELECT *select; ///<created in optimisation phase
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JOIN_TAB *return_tab; ///<used only for outer joins
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Item **ref_pointer_array; ///<used pointer reference for this select
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@ -1689,6 +1695,7 @@ public:
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initialized= 0;
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cond_equal= 0;
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having_equal= 0;
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exec_const_cond= 0;
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group_optimized_away= 0;
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no_rows_in_result_called= 0;
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