MDEV-17023: Crash during read_histogram_for_table with optimizer_use_condition_selectivity set to 4

No need to read statistics for tables that are not USER tables.
We allocate memory for structures to collect statistics only for USER TABLES.

mysql-test/r/stat_tables.result

@@ -577,3 +577,16 @@ SELECT * FROM mysql.column_stats;
 db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
 DROP TABLE t1;
 set use_stat_tables=@save_use_stat_tables;
+#
+# MDEV-17023: Crash during read_histogram_for_table with optimizer_use_condition_selectivity set to 4
+#
+set @save_optimizer_use_condition_selectivity=@@optimizer_use_condition_selectivity;
+set @@optimizer_use_condition_selectivity=4;
+set @@use_stat_tables= PREFERABLY;
+explain
+SELECT * FROM INFORMATION_SCHEMA.PROFILING, mysql.user;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	PROFILING	ALL	NULL	NULL	NULL	NULL	NULL	
+1	SIMPLE	user	ALL	NULL	NULL	NULL	NULL	4	Using join buffer (flat, BNL join)
+set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+set use_stat_tables=@save_use_stat_tables;

mysql-test/r/stat_tables_innodb.result

@@ -604,5 +604,18 @@ SELECT * FROM mysql.column_stats;
 db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
 DROP TABLE t1;
 set use_stat_tables=@save_use_stat_tables;
+#
+# MDEV-17023: Crash during read_histogram_for_table with optimizer_use_condition_selectivity set to 4
+#
+set @save_optimizer_use_condition_selectivity=@@optimizer_use_condition_selectivity;
+set @@optimizer_use_condition_selectivity=4;
+set @@use_stat_tables= PREFERABLY;
+explain
+SELECT * FROM INFORMATION_SCHEMA.PROFILING, mysql.user;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	PROFILING	ALL	NULL	NULL	NULL	NULL	NULL	
+1	SIMPLE	user	ALL	NULL	NULL	NULL	NULL	4	Using join buffer (flat, BNL join)
+set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+set use_stat_tables=@save_use_stat_tables;
 set optimizer_switch=@save_optimizer_switch_for_stat_tables_test;
 SET SESSION STORAGE_ENGINE=DEFAULT;

mysql-test/t/stat_tables.test

@@ -356,3 +356,15 @@ SELECT * FROM mysql.column_stats;
 DROP TABLE t1;
 
 set use_stat_tables=@save_use_stat_tables;
+
+--echo #
+--echo # MDEV-17023: Crash during read_histogram_for_table with optimizer_use_condition_selectivity set to 4
+--echo #
+
+set @save_optimizer_use_condition_selectivity=@@optimizer_use_condition_selectivity;
+set @@optimizer_use_condition_selectivity=4;
+set @@use_stat_tables= PREFERABLY;
+explain
+SELECT * FROM INFORMATION_SCHEMA.PROFILING, mysql.user;
+set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+set use_stat_tables=@save_use_stat_tables;

sql/sql_statistics.cc

@@ -3129,6 +3129,9 @@ int read_statistics_for_tables_if_needed(THD *thd, TABLE_LIST *tables)
     if (!tl->is_view_or_derived() && !is_temporary_table(tl) && tl->table)
     { 
       TABLE_SHARE *table_share= tl->table->s;
+      if (table_share && !(table_share->table_category == TABLE_CATEGORY_USER))
+        continue;
+
       if (table_share && 
           table_share->stats_cb.stats_can_be_read &&
 	  !table_share->stats_cb.stats_is_read)