Fix for BUG#46384 - mysqld segfault when trying to create table with same

                    name as existing view

When trying to create a table with the same name as existing view with
join, mysql server crashes.

The problem is when create table is issued with the same name as view, while
verifying with the existing tables, we assume that base table object is 
created always.

In this case, since it is a view over multiple tables, we don't have the 
mysql derived table object.

Fixed the logic which checks if there is an existing table to not to assume
that table object is created when the base table is view over multiple 
tables.

mysql-test/r/create.result:
  BUG#46384 - mysqld segfault when trying to create table with same 
              name as existing view
  
  Testcase for the bug
mysql-test/t/create.test:
  BUG#46384 - mysqld segfault when trying to create table with same 
              name as existing view
  
  Testcase for the bug
sql/sql_insert.cc:
  BUG#46384 - mysqld segfault when trying to create table with same 
                  name as existing view
      
  Fixed create_table_from_items() method to properly check, if the base table 
  is a view over multiple tables.

mysql-test/r/create.result

@@ -1559,4 +1559,17 @@ CREATE TABLE IF NOT EXISTS t2 (a INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY)
 SELECT a FROM t1;
 ERROR 23000: Duplicate entry '1' for key 1
 DROP TABLE t1, t2;
+#
+# BUG#46384 - mysqld segfault when trying to create table with same 
+#             name as existing view
+#
+CREATE TABLE t1 (a INT);
+CREATE TABLE t2 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3);
+INSERT INTO t2 VALUES (1),(2),(3);
+CREATE VIEW v1 AS SELECT t1.a FROM t1, t2;
+CREATE TABLE v1 AS SELECT * FROM t1;
+ERROR 42S01: Table 'v1' already exists
+DROP VIEW v1;
+DROP TABLE t1,t2;
 End of 5.0 tests

mysql-test/t/create.test

@@ -1194,5 +1194,22 @@ CREATE TABLE IF NOT EXISTS t2 (a INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY)
 
 DROP TABLE t1, t2;
 
+--echo #
+--echo # BUG#46384 - mysqld segfault when trying to create table with same 
+--echo #             name as existing view
+--echo #
+
+CREATE TABLE t1 (a INT);
+CREATE TABLE t2 (a INT);
+
+INSERT INTO t1 VALUES (1),(2),(3);
+INSERT INTO t2 VALUES (1),(2),(3);
+
+CREATE VIEW v1 AS SELECT t1.a FROM t1, t2;
+--error ER_TABLE_EXISTS_ERROR
+CREATE TABLE v1 AS SELECT * FROM t1;
+
+DROP VIEW v1;
+DROP TABLE t1,t2;
 
 --echo End of 5.0 tests

sql/sql_insert.cc

@@ -3217,7 +3217,7 @@ static TABLE *create_table_from_items(THD *thd, HA_CREATE_INFO *create_info,
   DBUG_EXECUTE_IF("sleep_create_select_before_check_if_exists", my_sleep(6000000););
 
   if (!(create_info->options & HA_LEX_CREATE_TMP_TABLE) &&
-      create_table->table->db_stat)
+      (create_table->table && create_table->table->db_stat))
   {
     /* Table already exists and was open at open_and_lock_tables() stage. */
     if (create_info->options & HA_LEX_CREATE_IF_NOT_EXISTS)