MDEV-5535: Cannot reopen temporary table

Since a query can now refer to the same temporary table
multiple times, find_dup_table()/find_table_in_list()
have been updated to also consider this new possibility.

mysql-test/r/reopen_temp_table.result

@@ -151,5 +151,18 @@ SELECT COUNT(*) FROM t4;
 COUNT(*)
 4
 DROP TABLE t4;
+CREATE TABLE t5 (a INT) ENGINE=INNODB;
+CREATE TEMPORARY TABLE t6 (a INT) ENGINE=INNODB;
+INSERT INTO t5 VALUES(1), (2);
+INSERT INTO t6 SELECT * FROM t5;
+INSERT INTO t6 SELECT * FROM t6;
+INSERT INTO t5 SELECT * FROM t6;
+SELECT COUNT(*)=6 FROM t5;
+COUNT(*)=6
+1
+SELECT COUNT(*)=4 FROM t6;
+COUNT(*)=4
+1
+DROP TABLE t5, t6;
 # Cleanup
 DROP DATABASE temp_db;

mysql-test/t/reopen_temp_table.test

@@ -149,5 +149,15 @@ INSERT INTO t4 SELECT * FROM t4;
 SELECT COUNT(*) FROM t4;
 DROP TABLE t4;
 
+CREATE TABLE t5 (a INT) ENGINE=INNODB;
+CREATE TEMPORARY TABLE t6 (a INT) ENGINE=INNODB;
+INSERT INTO t5 VALUES(1), (2);
+INSERT INTO t6 SELECT * FROM t5;
+INSERT INTO t6 SELECT * FROM t6;
+INSERT INTO t5 SELECT * FROM t6;
+SELECT COUNT(*)=6 FROM t5;
+SELECT COUNT(*)=4 FROM t6;
+DROP TABLE t5, t6;
+
 --echo # Cleanup
 DROP DATABASE temp_db;

sql/sql_base.cc

@@ -910,8 +910,7 @@ TABLE_LIST *find_table_in_list(TABLE_LIST *table,
 {
   for (; table; table= table->*link )
   {
-    if ((table->table == 0 || table->table->s->tmp_table == NO_TMP_TABLE) &&
-        strcmp(table->db, db_name) == 0 &&
+    if (strcmp(table->db, db_name) == 0 &&
         strcmp(table->table_name, table_name) == 0)
       break;
   }
@@ -976,9 +975,6 @@ TABLE_LIST* find_dup_table(THD *thd, TABLE_LIST *table, TABLE_LIST *table_list,
     /* All MyISAMMRG children are plain MyISAM tables. */
     DBUG_ASSERT(table->table->file->ht->db_type != DB_TYPE_MRG_MYISAM);
 
-    /* temporary table is always unique */
-    if (table->table && table->table->s->tmp_table != NO_TMP_TABLE)
-      DBUG_RETURN(0);
     table= table->find_underlying_table(table->table);
     /*
       as far as we have table->table we have to find real TABLE_LIST of