MDEV-6888: Query spends a long time in best_extension_by_limited_search with mrr enabled

- TABLE::create_key_part_by_field() should not set PART_KEY_FLAG in field->flags
  = The reason is that it is used by hash join code which calls it to create a hash
    table lookup structure. It doesn't create a real index.
  = Another caller of the function is TABLE::add_tmp_key(). Made it to set the flag itself.

- The differences in join_cache.result could also be observed before this patch: one
  could put "FLUSH TABLES" before the queries and get exactly the same difference.

mysql-test/r/join_cache.result

@@ -498,8 +498,8 @@ CountryLanguage.Percentage > 50 AND
 LENGTH(Language) < LENGTH(City.Name) - 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	Country	ALL	NULL	NULL	NULL	NULL	239	Using where
-1	SIMPLE	City	ALL	NULL	NULL	NULL	NULL	4079	Using where; Using join buffer (flat, BNL join)
 1	SIMPLE	CountryLanguage	ALL	NULL	NULL	NULL	NULL	984	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	City	ALL	NULL	NULL	NULL	NULL	4079	Using where; Using join buffer (flat, BNL join)
 SELECT City.Name, Country.Name, CountryLanguage.Language
 FROM City,Country,CountryLanguage
 WHERE City.Country=Country.Code AND
@@ -576,8 +576,8 @@ CountryLanguage.Percentage > 50 AND
 LENGTH(Language) < LENGTH(City.Name) - 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	Country	ALL	NULL	NULL	NULL	NULL	239	Using where
-1	SIMPLE	City	ALL	NULL	NULL	NULL	NULL	4079	Using where; Using join buffer (flat, BNL join)
-1	SIMPLE	CountryLanguage	ALL	NULL	NULL	NULL	NULL	984	Using where; Using join buffer (incremental, BNL join)
+1	SIMPLE	CountryLanguage	ALL	NULL	NULL	NULL	NULL	984	Using where; Using join buffer (flat, BNL join)
+1	SIMPLE	City	ALL	NULL	NULL	NULL	NULL	4079	Using where; Using join buffer (incremental, BNL join)
 SELECT City.Name, Country.Name, CountryLanguage.Language
 FROM City,Country,CountryLanguage
 WHERE City.Country=Country.Code AND
@@ -654,8 +654,8 @@ CountryLanguage.Percentage > 50 AND
 LENGTH(Language) < LENGTH(City.Name) - 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	Country	ALL	NULL	NULL	NULL	NULL	239	Using where
-1	SIMPLE	City	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	4079	Using where; Using join buffer (flat, BNLH join)
 1	SIMPLE	CountryLanguage	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	984	Using where; Using join buffer (flat, BNLH join)
+1	SIMPLE	City	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	4079	Using where; Using join buffer (flat, BNLH join)
 SELECT City.Name, Country.Name, CountryLanguage.Language
 FROM City,Country,CountryLanguage
 WHERE City.Country=Country.Code AND
@@ -732,8 +732,8 @@ CountryLanguage.Percentage > 50 AND
 LENGTH(Language) < LENGTH(City.Name) - 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	Country	ALL	NULL	NULL	NULL	NULL	239	Using where
-1	SIMPLE	City	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	4079	Using where; Using join buffer (flat, BNLH join)
-1	SIMPLE	CountryLanguage	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	984	Using where; Using join buffer (incremental, BNLH join)
+1	SIMPLE	CountryLanguage	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	984	Using where; Using join buffer (flat, BNLH join)
+1	SIMPLE	City	hash_ALL	NULL	#hash#$hj	3	world.Country.Code	4079	Using where; Using join buffer (incremental, BNLH join)
 SELECT City.Name, Country.Name, CountryLanguage.Language
 FROM City,Country,CountryLanguage
 WHERE City.Country=Country.Code AND

mysql-test/r/join_outer.result

@@ -1920,4 +1920,27 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	select `test`.`t1`.`i1` AS `i1`,`test`.`t2`.`i2` AS `i2`,`test`.`t3`.`i3` AS `i3`,`test`.`t3`.`d3` AS `d3` from `test`.`t1` left join (`test`.`t2` join `test`.`t3`) on(((`test`.`t2`.`i2` = `test`.`t1`.`i1`) and (`test`.`t3`.`i3` = `test`.`t1`.`i1`))) where ((`test`.`t3`.`d3` = 0) or isnull(`test`.`t3`.`d3`))
 DROP TABLE t1,t2,t3;
+#
+# Bug mdev-6705: wrong on expression after constant row substitution 
+#                that triggers a simplification of WHERE condition
+#
+CREATE TABLE t1 (a int, b int) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (10,8);
+CREATE TABLE t2 (c int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (8),(9);
+CREATE TABLE t3 (d int) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (3),(8);
+EXPLAIN EXTENDED
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select 10 AS `a`,8 AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t3`.`d` AS `d` from `test`.`t1` join `test`.`t2` left join `test`.`t3` on((`test`.`t3`.`d` = 10)) where ((`test`.`t2`.`c` = 8) and (`test`.`t3`.`d` = 8))
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+a	b	c	d
+DROP TABLE t1,t2,t3;
 SET optimizer_switch=@save_optimizer_switch;

mysql-test/r/join_outer_jcl6.result

@@ -1931,6 +1931,29 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	select `test`.`t1`.`i1` AS `i1`,`test`.`t2`.`i2` AS `i2`,`test`.`t3`.`i3` AS `i3`,`test`.`t3`.`d3` AS `d3` from `test`.`t1` left join (`test`.`t2` join `test`.`t3`) on(((`test`.`t2`.`i2` = `test`.`t1`.`i1`) and (`test`.`t3`.`i3` = `test`.`t1`.`i1`))) where ((`test`.`t3`.`d3` = 0) or isnull(`test`.`t3`.`d3`))
 DROP TABLE t1,t2,t3;
+#
+# Bug mdev-6705: wrong on expression after constant row substitution 
+#                that triggers a simplification of WHERE condition
+#
+CREATE TABLE t1 (a int, b int) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (10,8);
+CREATE TABLE t2 (c int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (8),(9);
+CREATE TABLE t3 (d int) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (3),(8);
+EXPLAIN EXTENDED
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; Using join buffer (flat, BNL join)
+Warnings:
+Note	1003	select 10 AS `a`,8 AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t3`.`d` AS `d` from `test`.`t1` join `test`.`t2` left join `test`.`t3` on((`test`.`t3`.`d` = 10)) where ((`test`.`t2`.`c` = 8) and (`test`.`t3`.`d` = 8))
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+WHERE b IN (1,2,3) OR b = d;
+a	b	c	d
+DROP TABLE t1,t2,t3;
 SET optimizer_switch=@save_optimizer_switch;
 set join_cache_level=default;
 show variables like 'join_cache_level';

mysql-test/t/derived_opt.test

 # Initialize
 --disable_warnings
-drop table if exists t1,t2,t3;
+drop table if exists t0,t1,t2,t3;
+drop database if exists test1;
 --enable_warnings
 
 set @exit_optimizer_switch=@@optimizer_switch;
@@ -272,5 +273,66 @@ limit 10;
 
 drop table t1, t2, t3, t4;
 
+--echo #
+--echo # MDEV-6888: Query spends a long time in best_extension_by_limited_search with mrr enabled
+--echo #
+create database test1;
+use test1;
+
+set @tmp_jcl= @@join_cache_level;
+set @tmp_os= @@optimizer_switch;
+set join_cache_level=8;
+set optimizer_switch='mrr=on,mrr_sort_keys=on';
+
+CREATE TABLE t0 (
+  f1 bigint(20) DEFAULT NULL,
+  f2 char(50) DEFAULT NULL
+) ENGINE=MEMORY DEFAULT CHARSET=latin1;
+INSERT INTO t0 VALUES (NULL,'numeric column is NULL'),(0,NULL),(5,'five'),(1,'one'),(2,'two');
+
+CREATE TABLE t1 (
+  f1 decimal(64,30) DEFAULT NULL,
+  f2 varchar(50) DEFAULT NULL
+) ENGINE=MEMORY DEFAULT CHARSET=latin1;
+
+INSERT INTO t1 VALUES 
+(NULL,'numeric column is NULL'),
+(0.000000000000000000000000000000,NULL),
+(5.000000000000000000000000000000,'five'),
+(1.000000000000000000000000000000,'one'),
+(3.000000000000000000000000000000,'three');
+
+CREATE TABLE t2 (
+  f1 double DEFAULT NULL,
+  f2 varbinary(50) DEFAULT NULL
+) ENGINE=MEMORY DEFAULT CHARSET=latin1;
+INSERT INTO t2 VALUES (NULL,'numeric column is NULL'),(0,NULL),(5,'five'),(2,'two'),(3,'three');
+
+create VIEW v0  AS select f1,f2 from t1 ;
+
+let $cnt= 27; 
+while ($cnt)
+{
+# i runs from 1 to 27
+  let $i= `select 28 - $cnt`;
+  let $prev=`select $i - 1`;
+
+# rem = i mod 3
+  let $rem= `select MOD($i, 3)`;
+# view uses $i, $prev and $rem:
+  eval create VIEW v$i AS select tab1_v$i.f1,tab1_v$i.f2 from t$rem tab1_v$i join v$prev tab2 on tab1_v$i.f1 = tab2.f1 and tab1_v$i.f2 = tab2.f2;
+  dec $cnt;
+}
+
+EXPLAIN SELECT CAST(f1 AS SIGNED INTEGER) AS f1, CAST(f2 AS CHAR) AS f2 FROM v27;
+--echo # This used to hang forever:
+EXPLAIN SELECT CAST(f1 AS SIGNED INTEGER) AS f1, CAST(f2 AS CHAR) AS f2 FROM v27;
+
+use test;
+drop database test1;
+set join_cache_level=@tmp_jcl;
+set optimizer_switch=@tmp_os;
+
+
 # The following command must be the last one the file 
 set optimizer_switch=@exit_optimizer_switch;

mysql-test/t/join_outer.test

@@ -1463,4 +1463,28 @@ SELECT * FROM t1 LEFT JOIN t2 LEFT JOIN t3 ON i2 = i3 ON i1 = i3
 
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # Bug mdev-6705: wrong on expression after constant row substitution 
+--echo #                that triggers a simplification of WHERE condition
+--echo #
+
+CREATE TABLE t1 (a int, b int) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (10,8);
+
+CREATE TABLE t2 (c int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (8),(9);
+
+CREATE TABLE t3 (d int) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (3),(8);
+
+EXPLAIN EXTENDED
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+  WHERE b IN (1,2,3) OR b = d;
+
+SELECT * FROM t1 INNER JOIN t2 ON c = b LEFT JOIN t3 ON d = a
+  WHERE b IN (1,2,3) OR b = d;
+
+DROP TABLE t1,t2,t3;
+
+
 SET optimizer_switch=@save_optimizer_switch;

sql/sql_select.cc

@@ -3530,6 +3530,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
   join->impossible_where= false;
   if (conds && const_count)
   { 
+    COND_EQUAL *orig_cond_equal = join->cond_equal;
     conds->update_used_tables();
     conds= remove_eq_conds(join->thd, conds, &join->cond_value);
     if (conds && conds->type() == Item::COND_ITEM &&
@@ -3556,7 +3557,21 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
         join->cond_equal->current_level.empty();
         join->cond_equal->current_level.push_back((Item_equal*) conds);
       }
-    }     
+    }
+
+    if (orig_cond_equal != join->cond_equal)
+    {
+      /*
+        If join->cond_equal has changed all references to it from COND_EQUAL
+        objects associated with ON expressions must be updated.
+      */
+      for (JOIN_TAB **pos=stat_vector+const_count ; (s= *pos) ; pos++) 
+      {
+        if (*s->on_expr_ref && s->cond_equal &&
+	    s->cond_equal->upper_levels == orig_cond_equal)
+          s->cond_equal->upper_levels= join->cond_equal;
+      }
+    }
   }
 
   /* Calc how many (possible) matched records in each table */
@@ -11999,10 +12014,18 @@ Item *eliminate_item_equal(COND *cond, COND_EQUAL *upper_levels,
     if (upper)
     {
       TABLE_LIST *native_sjm= embedding_sjm(item_equal->context_field);
-      if (item_const && upper->get_const())
+      Item *upper_const= upper->get_const();
+      if (item_const && upper_const)
       {
-        /* Upper item also has "field_item=const". Don't produce equality here */
-        item= 0;
+        /* 
+          Upper item also has "field_item=const".
+          Don't produce equality if const is equal to item_const.
+        */
+        Item_func_eq *func= new Item_func_eq(item_const, upper_const);
+        func->set_cmp_func();
+        func->quick_fix_field();
+        if (func->val_int())
+          item= 0;
       }
       else
       {

sql/table.cc

@@ -5401,7 +5401,6 @@ void TABLE::create_key_part_by_field(KEY *keyinfo,
                                      KEY_PART_INFO *key_part_info,
                                      Field *field, uint fieldnr)
 {   
-  field->flags|= PART_KEY_FLAG;
   key_part_info->null_bit= field->null_bit;
   key_part_info->null_offset= (uint) (field->null_ptr -
                                       (uchar*) record[0]);
@@ -5552,6 +5551,7 @@ bool TABLE::add_tmp_key(uint key, uint key_parts,
       (*reg_field)->key_start.set_bit(key);
     (*reg_field)->part_of_key.set_bit(key);
     create_key_part_by_field(keyinfo, key_part_info, *reg_field, fld_idx+1);
+    (*reg_field)->flags|= PART_KEY_FLAG;
     key_start= FALSE;
     key_part_info++;
   }