Bug#22331: Wrong WHERE in EXPLAIN EXTENDED when all expressions were optimized

away.

During optimization stage the WHERE conditions can be changed or even
be removed at all if they know for sure to be true of false. Thus they aren't
showed in the EXPLAIN EXTENDED which prints conditions after optimization.

Now if all elements of an Item_cond were removed this Item_cond is substituted
for an Item_int with the int value of the Item_cond.
If there were conditions that were totally optimized away then values of the
saved cond_value and having_value will be printed instead.

mysql-test/r/explain.result

@@ -57,3 +57,32 @@ select 3 into @v1;
 explain select 3 into @v1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+create table t1(f1 int, f2 int);
+insert into t1 values (1,1);
+create view v1 as select * from t1 where f1=1;
+explain extended select * from v1 where f2=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+Warnings:
+Note	1003	select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` where 1
+explain extended select * from t1 where 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+Warnings:
+Note	1003	select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` where 0
+explain extended select * from t1 where 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+Warnings:
+Note	1003	select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` where 1
+explain extended select * from t1 having 0;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING
+Warnings:
+Note	1003	select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` having 0
+explain extended select * from t1 having 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	
+Warnings:
+Note	1003	select `test`.`t1`.`f1` AS `f1`,`test`.`t1`.`f2` AS `f2` from `test`.`t1` having 1
+drop table t1;

mysql-test/r/func_test.result

@@ -79,7 +79,7 @@ explain extended select * from t1 where 1 xor 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 Warnings:
-Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1`
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where 0
 select - a from t1;
 - a
 -1

mysql-test/r/subselect.result

@@ -421,7 +421,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 3	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
-Note	1003	select 1 AS `1` from `test`.`t1`
+Note	1003	select 1 AS `1` from `test`.`t1` where 1
 drop table t1;
 CREATE TABLE `t1` (
 `numeropost` mediumint(8) unsigned NOT NULL auto_increment,
@@ -1180,7 +1180,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 Warnings:
-Note	1003	select <in_optimizer>(0,<exists>(select 1 AS `Not_used` from `test`.`t1` `a`)) AS `0 IN (SELECT 1 FROM t1 a)`
+Note	1003	select <in_optimizer>(0,<exists>(select 1 AS `Not_used` from `test`.`t1` `a` where 0)) AS `0 IN (SELECT 1 FROM t1 a)`
 INSERT INTO t1 (pseudo) VALUES ('test1');
 SELECT 0 IN (SELECT 1 FROM t1 a);
 0 IN (SELECT 1 FROM t1 a)
@@ -1190,7 +1190,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 Warnings:
-Note	1003	select <in_optimizer>(0,<exists>(select 1 AS `Not_used` from `test`.`t1` `a`)) AS `0 IN (SELECT 1 FROM t1 a)`
+Note	1003	select <in_optimizer>(0,<exists>(select 1 AS `Not_used` from `test`.`t1` `a` where 0)) AS `0 IN (SELECT 1 FROM t1 a)`
 drop table t1;
 CREATE TABLE `t1` (
 `i` int(11) NOT NULL default '0',
@@ -1532,7 +1532,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 Warnings:
-Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3`
+Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` where 0
 select * from t3 where NULL >= any (select b from t2 group by 1);
 a
 explain extended select * from t3 where NULL >= any (select b from t2 group by 1);
@@ -1540,7 +1540,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 Warnings:
-Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3`
+Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` where 0
 select * from t3 where NULL >= some (select b from t2);
 a
 explain extended select * from t3 where NULL >= some (select b from t2);
@@ -1548,7 +1548,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 Warnings:
-Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3`
+Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` where 0
 select * from t3 where NULL >= some (select b from t2 group by 1);
 a
 explain extended select * from t3 where NULL >= some (select b from t2 group by 1);
@@ -1556,7 +1556,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 Warnings:
-Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3`
+Note	1003	select `test`.`t3`.`a` AS `a` from `test`.`t3` where 0
 insert into t2 values (2,2), (2,1), (3,3), (3,1);
 select * from t3 where a > all (select max(b) from t2 group by a);
 a
@@ -1618,7 +1618,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 3	UNION	t1	system	NULL	NULL	NULL	NULL	1	
 NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
 Warnings:
-Note	1003	select `test`.`t1`.`s1` AS `s1` from `test`.`t1`
+Note	1003	select `test`.`t1`.`s1` AS `s1` from `test`.`t1` where 1
 drop table t1;
 CREATE TABLE t1 (number char(11) NOT NULL default '') ENGINE=MyISAM CHARSET=latin1;
 INSERT INTO t1 VALUES ('69294728265'),('18621828126'),('89356874041'),('95895001874');

mysql-test/t/explain.test

@@ -51,4 +51,18 @@ set names latin1;
 select 3 into @v1;
 explain select 3 into @v1;
 
+#
+# Bug#22331: Wrong WHERE in EXPLAIN EXTENDED when all expressions were
+#            optimized away.
+#
+create table t1(f1 int, f2 int);
+insert into t1 values (1,1);
+create view v1 as select * from t1 where f1=1;
+explain extended select * from v1 where f2=1;
+explain extended select * from t1 where 0;
+explain extended select * from t1 where 1;
+explain extended select * from t1 having 0;
+explain extended select * from t1 having 1;
+drop table t1;
+
 # End of 5.0 tests.

sql/sql_lex.cc

@@ -1192,6 +1192,7 @@ void st_select_lex::init_select()
   is_correlated= 0;
   cur_pos_in_select_list= UNDEF_POS;
   non_agg_fields.empty();
+  cond_value= having_value= Item::COND_UNDEF;
 }
 
 /*

sql/sql_lex.h

@@ -487,6 +487,8 @@ class st_select_lex: public st_select_lex_node
   Item *where, *having;                         /* WHERE & HAVING clauses */
   Item *prep_where; /* saved WHERE clause for prepared statement processing */
   Item *prep_having;/* saved HAVING clause for prepared statement processing */
+  /* Saved values of the WHERE and HAVING clauses*/
+  Item::cond_result cond_value, having_value;
   /* point on lex in which it was created, used in view subquery detection */
   st_lex *parent_lex;
   enum olap_type olap;

sql/sql_select.cc

@@ -681,7 +681,6 @@ JOIN::optimize()
   }
 
   {
-    Item::cond_result having_value;
     having= optimize_cond(this, having, join_list, &having_value);
     if (thd->net.report_error)
     {
@@ -689,6 +688,10 @@ JOIN::optimize()
       DBUG_PRINT("error",("Error from optimize_cond"));
       DBUG_RETURN(1);
     }
+    if (select_lex->where)
+      select_lex->cond_value= cond_value;
+    if (select_lex->having)
+      select_lex->having_value= having_value;
 
     if (cond_value == Item::COND_FALSE || having_value == Item::COND_FALSE || 
         (!unit->select_limit_cnt && !(select_options & OPTION_FOUND_ROWS)))
@@ -829,6 +832,7 @@ JOIN::optimize()
     conds->update_used_tables();
     DBUG_EXECUTE("where", print_where(conds, "after substitute_best_equal"););
   }
+
   /*
     Permorm the the optimization on fields evaluation mentioned above
     for all on expressions.
@@ -7535,6 +7539,9 @@ static COND* substitute_for_best_equal_field(COND *cond,
           break;
       }
     }
+    if (!((Item_cond*)cond)->argument_list()->elements)
+      cond= new Item_int(cond->val_bool());
+
   }
   else if (cond->type() == Item::FUNC_ITEM && 
            ((Item_cond*) cond)->functype() == Item_func::MULT_EQUAL_FUNC)
@@ -15259,10 +15266,13 @@ void st_select_lex::print(THD *thd, String *str)
   Item *cur_where= where;
   if (join)
     cur_where= join->conds;
-  if (cur_where)
+  if (cur_where || cond_value != Item::COND_UNDEF)
   {
     str->append(STRING_WITH_LEN(" where "));
-    cur_where->print(str);
+    if (cur_where)
+      cur_where->print(str);
+    else
+      str->append(cond_value != Item::COND_FALSE ? "1" : "0");
   }
 
   // group by & olap
@@ -15288,10 +15298,13 @@ void st_select_lex::print(THD *thd, String *str)
   if (join)
     cur_having= join->having;
 
-  if (cur_having)
+  if (cur_having || having_value != Item::COND_UNDEF)
   {
     str->append(STRING_WITH_LEN(" having "));
-    cur_having->print(str);
+    if (cur_having)
+      cur_having->print(str);
+    else
+      str->append(having_value != Item::COND_FALSE ? "1" : "0");
   }
 
   if (order_list.elements)

sql/sql_select.h

@@ -292,7 +292,7 @@ class JOIN :public Sql_alloc
 
   bool need_tmp, hidden_group_fields;
   DYNAMIC_ARRAY keyuse;
-  Item::cond_result cond_value;
+  Item::cond_result cond_value, having_value;
   List<Item> all_fields; // to store all fields that used in query
   //Above list changed to use temporary table
   List<Item> tmp_all_fields1, tmp_all_fields2, tmp_all_fields3;