MDEV-19198 - DBUG assert in CREATE IF NOT EXIST under LOCK TABLES WRITE

Fixed the ASSERT to take care of the case when table already existed.

mysql-test/main/lock.result

@@ -535,3 +535,25 @@ DROP TABLE t;
 #
 # End of 10.5 tests
 #
+#
+# MDEV-19198 Assertion `(create_info->tmp_table()) || ....`
+# failed in mysql_create_like_table
+#
+CREATE TABLE t1 (c INT);
+CREATE TABLE t2 (c INT);
+LOCK TABLES t1 WRITE, t2 READ;
+CREATE TABLE IF NOT EXISTS t1 LIKE t2;
+Warnings:
+Note	1050	Table 't1' already exists
+UNLOCK TABLES;
+LOCK TABLES t1 READ , t2 READ;
+CREATE TABLE IF NOT EXISTS t1 LIKE t2;
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+UNLOCK TABLES;
+CREATE TABLE IF NOT EXISTS t1 LIKE t2;
+Warnings:
+Note	1050	Table 't1' already exists
+DROP TABLES t1,t2;
+#
+# End of 10.6 tests
+#

mysql-test/main/lock.test

@@ -651,3 +651,28 @@ DROP TABLE t;
 --echo #
 --echo # End of 10.5 tests
 --echo #
+
+--echo #
+--echo # MDEV-19198 Assertion `(create_info->tmp_table()) || ....`
+--echo # failed in mysql_create_like_table
+--echo #
+
+CREATE TABLE t1 (c INT);
+CREATE TABLE t2 (c INT);
+
+LOCK TABLES t1 WRITE, t2 READ;
+CREATE TABLE IF NOT EXISTS t1 LIKE t2;
+UNLOCK TABLES;
+
+LOCK TABLES t1 READ , t2 READ;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+CREATE TABLE IF NOT EXISTS t1 LIKE t2;
+UNLOCK TABLES;
+
+CREATE TABLE IF NOT EXISTS t1 LIKE t2;
+
+DROP TABLES t1,t2;
+
+--echo #
+--echo # End of 10.6 tests
+--echo #

sql/sql_table.cc

@@ -4504,7 +4504,7 @@ warn:
   in various version of CREATE TABLE statement.
 
   @result
-    1 unspefied error
+    1 unspecifed error
     2 error; Don't log create statement
     0 ok
     -1 Table was used with IF NOT EXISTS and table existed (warning, not error)
@@ -5203,14 +5203,10 @@ bool mysql_create_like_table(THD* thd, TABLE_LIST* table,
   {
     /*
       Ensure that we have an exclusive lock on target table if we are creating
-      non-temporary table.
-      If we're creating non-temporary table, then either
-     - there is an exclusive lock on the table
-     or
-     - there was CREATE IF EXIST, and the table was not created
-      (it existed), and was previously locked
+      non-temporary table. We don't have or need the lock if the create failed
+      because of existing table when using "if exists".
     */
-    DBUG_ASSERT((create_info->tmp_table()) ||
+    DBUG_ASSERT((create_info->tmp_table()) || create_res < 0 ||
                 thd->mdl_context.is_lock_owner(MDL_key::TABLE, table->db.str,
                                                table->table_name.str,
                                                MDL_EXCLUSIVE) ||