Fixed crash in is_stat_table() when using hash joins.

Other usage if persistent statistics is checking 'stats_is_read' in
caller, which is why this was not noticed earlier.

Other things:
- Simplified no_stat_values_provided

mysql-test/main/analyze.result

@@ -417,5 +417,31 @@ test	t1	B	1	NULL
 test	t1	B	2	NULL
 drop table t1;
 #
+# Crash inis_eits_usable()
+#
+CREATE TABLE t1 (a int) ENGINE=MyISAM;
+CREATE TABLE t2 (b int) ENGINE=MyISAM;
+INSERT INTO t1 (a) VALUES (4), (6);
+INSERT INTO t2 (b) VALUES (0), (8);
+set @save_join_cache_level=@@join_cache_level;
+set @save_optimizer_switch=@@optimizer_switch;
+SET join_cache_level=3;
+SET optimizer_switch='join_cache_hashed=on';
+SET optimizer_switch='join_cache_bka=on';
+set optimizer_switch='hash_join_cardinality=on';
+select benchmark(1,1);
+benchmark(1,1)
+0
+EXPLAIN
+SELECT * FROM t1, t2 WHERE b=a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+1	SIMPLE	t2	hash_ALL	NULL	#hash#$hj	5	test.t1.a	2	Using where; Using join buffer (flat, BNLH join)
+SELECT * FROM t1, t2 WHERE b=a;
+a	b
+DROP TABLE t1,t2;
+set @@optimizer_switch=@save_optimizer_switch;
+set @@join_cache_level=@save_join_cache_level;
+#
 # End of 10.6 tests
 #

mysql-test/main/analyze.test

@@ -269,6 +269,33 @@ alter ignore table t1 rename key `b` to `B`, LOCK=shared;
 select * from mysql.index_stats where table_name= "t1";
 drop table t1;
 
+--echo #
+--echo # Crash inis_eits_usable()
+--echo #
+
+CREATE TABLE t1 (a int) ENGINE=MyISAM;
+
+CREATE TABLE t2 (b int) ENGINE=MyISAM;
+
+INSERT INTO t1 (a) VALUES (4), (6);
+INSERT INTO t2 (b) VALUES (0), (8);
+
+set @save_join_cache_level=@@join_cache_level;
+set @save_optimizer_switch=@@optimizer_switch;
+SET join_cache_level=3;
+SET optimizer_switch='join_cache_hashed=on';
+SET optimizer_switch='join_cache_bka=on';
+set optimizer_switch='hash_join_cardinality=on';
+
+select benchmark(1,1);
+EXPLAIN
+SELECT * FROM t1, t2 WHERE b=a;
+SELECT * FROM t1, t2 WHERE b=a;
+DROP TABLE t1,t2;
+
+set @@optimizer_switch=@save_optimizer_switch;
+set @@join_cache_level=@save_join_cache_level;
+
 --echo #
 --echo # End of 10.6 tests
 --echo #

sql/sql_statistics.cc

@@ -3125,7 +3125,8 @@ void TABLE_STATISTICS_CB::update_stats_in_table(TABLE *table)
   for ( ; *field_ptr; field_ptr++, column_stats++)
     (*field_ptr)->read_stats= column_stats;
   /* Mark that stats are now usable */
-  table->stats_is_read= true;
+  table->stats_is_read= (table->stats_cb->stats_available !=
+                         TABLE_STAT_NO_STATS);
 }
 
 
@@ -3246,8 +3247,6 @@ read_statistics_for_tables(THD *thd, TABLE_LIST *tables, bool force_reload)
       }
       mysql_mutex_unlock(&table_share->LOCK_statistics);
       table->stats_cb->update_stats_in_table(table);
-      table->stats_is_read= (stats_cb->stats_available !=
-                             TABLE_STAT_NO_STATS);
     }
   }
 
@@ -4312,11 +4311,9 @@ bool is_eits_usable(Field *field)
   Column_statistics* col_stats= field->read_stats;
   
   // check if column_statistics was allocated for this field
-  if (!col_stats)
+  if (!col_stats || !field->table->stats_is_read)
     return false;
 
-  DBUG_ASSERT(field->table->stats_is_read);
-
   /*
     (1): checks if we have EITS statistics for a particular column
     (2): Don't use EITS for GEOMETRY columns

sql/sql_statistics.h

@@ -445,9 +445,7 @@ class Column_statistics
   */
   bool no_stat_values_provided()
   {
-    if (column_stat_nulls == no_values_provided_bitmap())
-      return true;
-    return false;
+    return (column_stat_nulls == no_values_provided_bitmap());
   }
 };