MDEV-18460: Server crashed in strmake / tdc_create_key / THD::create_tmp_table_def_key

When there is a WITH clause we postpone check for tables without
database for later stages when tables in WITH will be defined.
But we should not try to open such tables as temporary tables because
temporary tables always belong to a some database.

mysql-test/r/cte_nonrecursive.result

@@ -1673,3 +1673,21 @@ with columns as (select 1 as t) select * from columns;
 t
 1
 use test;
+#
+# MDEV-18460: Server crashed in strmake / tdc_create_key /
+# THD::create_tmp_table_def_key
+#
+connect con1,localhost,root,,;
+CREATE TEMPORARY TABLE test.t (a INT);
+WITH cte AS (SELECT 1) SELECT * FROM cte;
+1
+1
+WITH t AS (SELECT 1) SELECT * FROM t;
+1
+1
+WITH cte AS (SELECT 1) SELECT * FROM t;
+ERROR 3D000: No database selected
+DROP TABLE test.t;
+connection default;
+disconnect con1;
+# End of 10.2 tests

mysql-test/t/cte_nonrecursive.test

@@ -1182,3 +1182,23 @@ with t as (select 1 as t) select * from t;
 with columns as (select 1 as t) select * from columns;
 
 use test;
+
+--echo #
+--echo # MDEV-18460: Server crashed in strmake / tdc_create_key /
+--echo # THD::create_tmp_table_def_key
+--echo #
+
+--connect con1,localhost,root,,
+--change_user root,,
+
+CREATE TEMPORARY TABLE test.t (a INT);
+WITH cte AS (SELECT 1) SELECT * FROM cte;
+WITH t AS (SELECT 1) SELECT * FROM t;
+--error ER_NO_DB_ERROR
+WITH cte AS (SELECT 1) SELECT * FROM t;
+DROP TABLE test.t;
+
+--connection default
+--disconnect con1
+
+--echo # End of 10.2 tests

sql/temporary_tables.cc

@@ -338,6 +338,13 @@ bool THD::open_temporary_table(TABLE_LIST *tl)
     DBUG_RETURN(false);
   }
 
+  if (!tl->db)
+  {
+    DBUG_PRINT("info",
+               ("Table reference to a temporary table must have database set"));
+    DBUG_RETURN(false);
+  }
+
   /*
     Temporary tables are not safe for parallel replication. They were
     designed to be visible to one thread only, so have no table locking.