Fix for bug#9383: INFORMATION_SCHEMA.COLUMNS, JOIN, Crash, prepared statement

   restore original 'lex->query_tables' table list after
   processing of information schema table
   remove unnecessary operations

mysql-test/r/ps.result

@@ -524,3 +524,21 @@ execute stmt using @a, @b, @c;
 a	b	c	a	b	c
 deallocate prepare stmt;
 drop table t1,t2;
+SET @aux= "SELECT COUNT(*)
+                FROM INFORMATION_SCHEMA.COLUMNS A,
+                INFORMATION_SCHEMA.COLUMNS B
+                WHERE A.TABLE_SCHEMA = B.TABLE_SCHEMA
+                AND A.TABLE_NAME = B.TABLE_NAME
+                AND A.COLUMN_NAME = B.COLUMN_NAME AND
+                A.TABLE_NAME = 'user'";
+prepare my_stmt from @aux;
+execute my_stmt;
+COUNT(*)
+37
+execute my_stmt;
+COUNT(*)
+37
+execute my_stmt;
+COUNT(*)
+37
+deallocate prepare my_stmt;

mysql-test/t/ps.test

@@ -540,3 +540,24 @@ deallocate prepare stmt;
 
 drop table t1,t2;
 
+
+#
+# Bug#9383: INFORMATION_SCHEMA.COLUMNS, JOIN, Crash, prepared statement
+#
+
+eval SET @aux= "SELECT COUNT(*)
+                FROM INFORMATION_SCHEMA.COLUMNS A,
+                INFORMATION_SCHEMA.COLUMNS B
+                WHERE A.TABLE_SCHEMA = B.TABLE_SCHEMA
+                AND A.TABLE_NAME = B.TABLE_NAME
+                AND A.COLUMN_NAME = B.COLUMN_NAME AND
+                A.TABLE_NAME = 'user'";
+
+let $exec_loop_count= 3;
+eval prepare my_stmt from @aux;
+while ($exec_loop_count)
+{
+  eval execute my_stmt;
+  dec $exec_loop_count;
+}
+deallocate prepare my_stmt;

sql/sql_lex.h

@@ -701,8 +701,9 @@ typedef struct st_lex
   TABLE_LIST *query_tables;	/* global list of all tables in this query */
   /*
     last element next_global of previous list (used only for list building
-    during parsing and VIEW processing. This pointer is not valid in
-    mysql_execute_command
+    during parsing and VIEW processing. This pointer could be invalid during
+    processing of information schema tables(see get_schema_tables_result
+    function)
   */
   TABLE_LIST **query_tables_last;
   TABLE_LIST *proc_table; /* refer to mysql.proc if it was opened by VIEW */

sql/sql_show.cc

@@ -3442,12 +3442,11 @@ 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())
     {
-      TABLE_LIST *save_next_global= table_list->next_global;
       TABLE_LIST **query_tables_last= lex->query_tables_last;
       TABLE *old_derived_tables= thd->derived_tables;
       MYSQL_LOCK *sql_lock= thd->lock;
       lex->sql_command= SQLCOM_SHOW_FIELDS;
-
+      DBUG_ASSERT(!*query_tables_last);
       if (&lex->unit != lex->current_select->master_unit()) // is subselect
       {
         table_list->table->file->extra(HA_EXTRA_RESET_STATE);
@@ -3466,8 +3465,8 @@ bool get_schema_tables_result(JOIN *join)
       thd->lock= sql_lock;
       lex->sql_command= SQLCOM_SELECT;
       thd->derived_tables= old_derived_tables;
-      table_list->next_global= save_next_global;
       lex->query_tables_last= query_tables_last;
+      *query_tables_last= 0;
     }
   }
   thd->no_warnings_for_error= 0;