Fix for bug#15307 GROUP_CONCAT() with ORDER BY returns empty set on information_schema(2nd ver)

  Fill schema tables with data before filesort if it's necessary

mysql-test/r/information_schema.result

@@ -1089,3 +1089,11 @@ create table mysqltest.t1(a int);
 select table_schema from information_schema.tables where table_schema='mysqltest';
 table_schema
 drop database mysqltest;
+select column_type, group_concat(table_schema, '.', table_name), count(*) as num
+from information_schema.columns where
+table_schema='information_schema' and
+(column_type = 'varchar(7)' or column_type = 'varchar(20)')
+group by column_type order by num;
+column_type	group_concat(table_schema, '.', table_name)	num
+varchar(20)	information_schema.COLUMNS	1
+varchar(7)	information_schema.ROUTINES,information_schema.VIEWS	2

mysql-test/t/information_schema.test

@@ -800,3 +800,12 @@ create table mysqltest.t1(a int);
 select table_schema from information_schema.tables where table_schema='mysqltest';
 --exec chmod +r $MYSQL_TEST_DIR/var/master-data/mysqltest
 drop database mysqltest;
+
+#
+# Bug#15307 GROUP_CONCAT() with ORDER BY returns empty set on information_schema
+#
+select column_type, group_concat(table_schema, '.', table_name), count(*) as num
+from information_schema.columns where
+table_schema='information_schema' and
+(column_type = 'varchar(7)' or column_type = 'varchar(20)')
+group by column_type order by num;

sql/sql_prepare.cc

@@ -2111,6 +2111,8 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
       were closed in the end of previous prepare or execute call.
     */
     tables->table= 0;
+    /* Reset is_schema_table_processed value(needed for I_S tables */
+    tables->is_schema_table_processed= FALSE;
 
     if (tables->prep_on_expr)
     {

sql/sql_select.cc

@@ -11582,6 +11582,12 @@ create_sort_index(THD *thd, JOIN *join, ORDER *order,
 	goto err;
     }
   }
+
+  /* Fill schema tables with data before filesort if it's necessary */
+  if ((join->select_lex->options & OPTION_SCHEMA_TABLE) &&
+      get_schema_tables_result(join))
+    goto err;
+
   if (table->s->tmp_table)
     table->file->info(HA_STATUS_VARIABLE);	// Get record count
   table->sort.found_records=filesort(thd, table,sortorder, length,

sql/sql_show.cc

@@ -3845,7 +3845,16 @@ bool get_schema_tables_result(JOIN *join)
     TABLE_LIST *table_list= tab->table->pos_in_table_list;
     if (table_list->schema_table && thd->fill_derived_tables())
     {
-      if (&lex->unit != lex->current_select->master_unit()) // is subselect
+      bool is_subselect= (&lex->unit != lex->current_select->master_unit());
+      /*
+        The schema table is already processed and 
+        the statement is not a subselect.
+        So we don't need to handle this table again.
+      */
+      if (table_list->is_schema_table_processed && !is_subselect)
+        continue;
+
+      if (is_subselect) // is subselect
       {
         table_list->table->file->extra(HA_EXTRA_RESET_STATE);
         table_list->table->file->delete_all_rows();
@@ -3858,6 +3867,7 @@ bool get_schema_tables_result(JOIN *join)
       if (table_list->schema_table->fill_table(thd, table_list,
                                                tab->select_cond))
         result= 1;
+      table_list->is_schema_table_processed= TRUE;
     }
   }
   thd->no_warnings_for_error= 0;

sql/table.h

@@ -515,6 +515,7 @@ typedef struct st_table_list
   st_select_lex_unit *derived;		/* SELECT_LEX_UNIT of derived table */
   ST_SCHEMA_TABLE *schema_table;        /* Information_schema table */
   st_select_lex	*schema_select_lex;
+  bool is_schema_table_processed;
   /*
     True when the view field translation table is used to convert
     schema table fields for backwards compatibility with SHOW command.