Fixed bug mdev-4370.

Don't try to a histogram if it is not read into the cache for statistical data.
It may happen so if optimizer_use_condition_selectivity is set to 3. This 
setting orders the optimizer not use histograms to calculate selectivity.

mysql-test/r/selectivity.result

@@ -794,4 +794,32 @@ SELECT 1 FROM t1, t2 WHERE pk = 6 AND a = 2 AND b = 10;
 1
 DROP TABLE t1,t2;
 set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+#
+# Bug mdev-4370: Histograms have bean created, but the query is run after
+#                FLUSH TABLES with optimizer_use_condition_selectivity=3
+#
+set use_stat_tables=PREFERABLY;
+set histogram_size=10;
+set histogram_type='SINGLE_PREC_HB';
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (9), (1);
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+FLUSH TABLES;
+set optimizer_use_condition_selectivity=3;
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	75.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where (`test`.`t1`.`a` > 3)
+SELECT * FROM t1 WHERE a > 3;
+a
+9
+set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+DROP TABLE t1;
+set histogram_size=@save_histogram_size;
+set histogram_type=@save_histogram_type;
+set use_stat_tables=@save_use_stat_tables;
 set use_stat_tables=@save_use_stat_tables;

mysql-test/r/selectivity_innodb.result

@@ -801,6 +801,34 @@ SELECT 1 FROM t1, t2 WHERE pk = 6 AND a = 2 AND b = 10;
 1
 DROP TABLE t1,t2;
 set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+#
+# Bug mdev-4370: Histograms have bean created, but the query is run after
+#                FLUSH TABLES with optimizer_use_condition_selectivity=3
+#
+set use_stat_tables=PREFERABLY;
+set histogram_size=10;
+set histogram_type='SINGLE_PREC_HB';
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (9), (1);
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+FLUSH TABLES;
+set optimizer_use_condition_selectivity=3;
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	75.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where (`test`.`t1`.`a` > 3)
+SELECT * FROM t1 WHERE a > 3;
+a
+9
+set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+DROP TABLE t1;
+set histogram_size=@save_histogram_size;
+set histogram_type=@save_histogram_type;
+set use_stat_tables=@save_use_stat_tables;
 set use_stat_tables=@save_use_stat_tables;
 set optimizer_switch=@save_optimizer_switch_for_selectivity_test;
 SET SESSION STORAGE_ENGINE=DEFAULT;

mysql-test/t/selectivity.test

@@ -384,5 +384,32 @@ DROP TABLE t1,t2;
 
 set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
 
+--echo #
+--echo # Bug mdev-4370: Histograms have bean created, but the query is run after
+--echo #                FLUSH TABLES with optimizer_use_condition_selectivity=3
+--echo #
+
+set use_stat_tables=PREFERABLY; 
+set histogram_size=10;
+set histogram_type='SINGLE_PREC_HB';
+
+CREATE TABLE t1 (a int);
+INSERT INTO t1 VALUES (9), (1);
+ANALYZE TABLE t1;
+FLUSH TABLES;
+
+set optimizer_use_condition_selectivity=3;
+
+EXPLAIN EXTENDED
+SELECT * FROM t1 WHERE a > 3;
+SELECT * FROM t1 WHERE a > 3;
+
+set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+
+DROP TABLE t1;
+
+set histogram_size=@save_histogram_size;
+set histogram_type=@save_histogram_type;
+set use_stat_tables=@save_use_stat_tables;
 
 set use_stat_tables=@save_use_stat_tables;

sql/sql_statistics.cc

@@ -3369,7 +3369,7 @@ double get_column_range_cardinality(Field *field,
           col_stats->min_value && col_stats->max_value)
       {
         Histogram *hist= &col_stats->histogram;
-        if (hist->get_size() > 0)
+        if (hist->is_available())
         {
           double pos= field->middle_point_pos(col_stats->min_value,
                                               col_stats->max_value);
@@ -3406,7 +3406,7 @@ double get_column_range_cardinality(Field *field,
         max_mp_pos= 1.0;
 
       Histogram *hist= &col_stats->histogram;
-      if (hist->get_size() == 0)
+      if (!hist->is_available())
         sel= (max_mp_pos - min_mp_pos);
       else
         sel= hist->range_selectivity(min_mp_pos, max_mp_pos);

sql/sql_statistics.h

@@ -195,6 +195,8 @@ class Histogram
 
   void set_values (uchar *vals) { values= (uchar *) vals; }
 
+  bool is_available() { return get_size() > 0 && get_values(); }
+
   void set_value(uint i, double val)
   {
     switch (type) {