Fix for BUG#20954: avg(keyval) retuns 0.38 but max(keyval) returns an empty set

The problem was in that opt_sum_query() replaced MIN/MAX functions
with the corresponding constant found in a key, but due to imprecise
representation of float numbers, when evaluating the where clause,
this comparison failed.

When MIN/MAX optimization detects that all tables can be removed,
also remove all conjuncts in a where clause that refer to these
tables. As a result of this fix, these conditions are not evaluated
twice, and in the case of float number comparisons we do not discard
result rows due to imprecise float representation.

As a side-effect this fix also corrects an unnoticed problem in
bug 12882.

mysql-test/r/func_group.result

@@ -824,6 +824,7 @@ select 1, min(a) from t1m where 1=99;
 1	NULL
 select 1, min(1) from t1m where a=99;
 1	min(1)
+1	NULL
 select 1, min(1) from t1m where 1=99;
 1	min(1)
 1	NULL
@@ -835,6 +836,7 @@ select 1, max(a) from t1m where 1=99;
 1	NULL
 select 1, max(1) from t1m where a=99;
 1	max(1)
+1	NULL
 select 1, max(1) from t1m where 1=99;
 1	max(1)
 1	NULL

mysql-test/r/select.result

@@ -2744,3 +2744,52 @@ SELECT i='1e+01',i=1e+01, i in (1e+01), i in ('1e+01') FROM t1;
 i='1e+01'	i=1e+01	i in (1e+01)	i in ('1e+01')
 0	1	1	1
 DROP TABLE t1;
+CREATE TABLE t1 (key1 float default NULL, UNIQUE KEY key1 (key1));
+CREATE TABLE t2 (key2 float default NULL, UNIQUE KEY key2 (key2));
+INSERT INTO t1 VALUES (0.3762),(0.3845),(0.6158),(0.7941);
+INSERT INTO t2 VALUES (1.3762),(1.3845),(1.6158),(1.7941);
+explain select max(key1) from t1 where key1 <= 0.6158;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select max(key2) from t2 where key2 <= 1.6158;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select min(key1) from t1 where key1 >= 0.3762;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select min(key2) from t2 where key2 >= 1.3762;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select max(key1), min(key2) from t1, t2
+where key1 <= 0.6158 and key2 >= 1.3762;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select max(key1) from t1 where key1 <= 0.6158 and rand() + 0.5 >= 0.5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select min(key1) from t1 where key1 >= 0.3762 and rand() + 0.5 >= 0.5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select max(key1) from t1 where key1 <= 0.6158;
+max(key1)
+0.61580002307892
+select max(key2) from t2 where key2 <= 1.6158;
+max(key2)
+1.6158000230789
+select min(key1) from t1 where key1 >= 0.3762;
+min(key1)
+0.37619999051094
+select min(key2) from t2 where key2 >= 1.3762;
+min(key2)
+1.3761999607086
+select max(key1), min(key2) from t1, t2
+where key1 <= 0.6158 and key2 >= 1.3762;
+max(key1)	min(key2)
+0.61580002307892	1.3761999607086
+select max(key1) from t1 where key1 <= 0.6158 and rand() + 0.5 >= 0.5;
+max(key1)
+0.61580002307892
+select min(key1) from t1 where key1 >= 0.3762 and rand() + 0.5 >= 0.5;
+min(key1)
+0.37619999051094
+DROP TABLE t1,t2;

mysql-test/r/subselect.result

@@ -539,7 +539,7 @@ EXPLAIN EXTENDED SELECT MAX(numreponse) FROM t1 WHERE numeropost='1';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select max(test.t1.numreponse) AS `MAX(numreponse)` from test.t1 where (test.t1.numeropost = _latin1'1')
+Note	1003	select max(test.t1.numreponse) AS `MAX(numreponse)` from test.t1
 EXPLAIN EXTENDED SELECT numreponse FROM t1 WHERE numeropost='1' AND numreponse=(SELECT MAX(numreponse) FROM t1 WHERE numeropost='1');
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	Using index

mysql-test/t/select.test

@@ -2297,4 +2297,34 @@ INSERT INTO t1 VALUES (10);
 SELECT i='1e+01',i=1e+01, i in (1e+01), i in ('1e+01') FROM t1;
 DROP TABLE t1;
 
+#
+# Bug #20954 "avg(keyval) retuns 0.38 but max(keyval) returns an empty set"
+#
+--disable_ps_protocol
+CREATE TABLE t1 (key1 float default NULL, UNIQUE KEY key1 (key1));
+CREATE TABLE t2 (key2 float default NULL, UNIQUE KEY key2 (key2));
+INSERT INTO t1 VALUES (0.3762),(0.3845),(0.6158),(0.7941);
+INSERT INTO t2 VALUES (1.3762),(1.3845),(1.6158),(1.7941);
+
+explain select max(key1) from t1 where key1 <= 0.6158;
+explain select max(key2) from t2 where key2 <= 1.6158;
+explain select min(key1) from t1 where key1 >= 0.3762;
+explain select min(key2) from t2 where key2 >= 1.3762;
+explain select max(key1), min(key2) from t1, t2
+where key1 <= 0.6158 and key2 >= 1.3762;
+explain select max(key1) from t1 where key1 <= 0.6158 and rand() + 0.5 >= 0.5;
+explain select min(key1) from t1 where key1 >= 0.3762 and rand() + 0.5 >= 0.5;
+
+select max(key1) from t1 where key1 <= 0.6158;
+select max(key2) from t2 where key2 <= 1.6158;
+select min(key1) from t1 where key1 >= 0.3762;
+select min(key2) from t2 where key2 >= 1.3762;
+select max(key1), min(key2) from t1, t2
+where key1 <= 0.6158 and key2 >= 1.3762;
+select max(key1) from t1 where key1 <= 0.6158 and rand() + 0.5 >= 0.5;
+select min(key1) from t1 where key1 >= 0.3762 and rand() + 0.5 >= 0.5;
+
+DROP TABLE t1,t2;
+--enable_ps_protocol
+
 # End of 4.1 tests

sql/sql_select.cc

@@ -547,6 +547,24 @@ JOIN::optimize()
       }
       zero_result_cause= "Select tables optimized away";
       tables_list= 0;				// All tables resolved
+      /*
+        Extract all table-independent conditions and replace the WHERE
+        clause with them. All other conditions were computed by opt_sum_query
+        and the MIN/MAX/COUNT function(s) have been replaced by constants,
+        so there is no need to compute the whole WHERE clause again.
+        Notice that make_cond_for_table() will always succeed to remove all
+        computed conditions, because opt_sum_query() is applicable only to
+        conjunctions.
+      */
+      if (conds)
+      {
+        COND *table_independent_conds=
+          make_cond_for_table(conds, PSEUDO_TABLE_BITS, 0);
+        DBUG_EXECUTE("where",
+                     print_where(table_independent_conds,
+                                 "where after opt_sum_query()"););
+        conds= table_independent_conds;
+      }
     }
   }
   if (!tables_list)