MDEV-18304 sql_safe_updates does not work with OR clauses

not every index-using plan sets bits in table->quick_keys.
QUICK_ROR_INTERSECT_SELECT, for example, doesn't.

Use the fact that select->quick is set instead.

Also allow EXPLAIN to work.

mysql-test/main/sql_safe_updates.result

+#
+# MDEV-14429 sql_safe_updates in my.cnf not work
+#
 select @@sql_safe_updates;
 @@sql_safe_updates
 1
+#
+# MDEV-18304 sql_safe_updates does not work with OR clauses
+#
+create table t1 (a int, b int, primary key (a), key (b));
+update t1 set b=2 where a=1 or b=2;
+ERROR HY000: You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
+explain update t1 set b=2 where a=1 or b=2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	1	Using where
+delete from t1 where a=1 or b=2;
+ERROR HY000: You are using safe update mode and you tried to update a table without a WHERE that uses a KEY column
+explain delete from t1 where a=1 or b=2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	1	Using where
+insert into t1 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8);
+update t1 set b=2 where a=1 or b=2;
+delete from t1 where a=1 or b=2;
+drop table t1;
+#
+# End of 10.3 tests
+#

mysql-test/main/sql_safe_updates.test

-#
-# MDEV-14429 sql_safe_updates in my.cnf not work
-#
+--echo #
+--echo # MDEV-14429 sql_safe_updates in my.cnf not work
+--echo #
 select @@sql_safe_updates;
+
+--echo #
+--echo # MDEV-18304 sql_safe_updates does not work with OR clauses
+--echo #
+create table t1 (a int, b int, primary key (a), key (b));
+--error ER_UPDATE_WITHOUT_KEY_IN_SAFE_MODE
+update t1 set b=2 where a=1 or b=2;
+explain update t1 set b=2 where a=1 or b=2;
+--error ER_UPDATE_WITHOUT_KEY_IN_SAFE_MODE
+delete from t1 where a=1 or b=2;
+explain delete from t1 where a=1 or b=2;
+insert into t1 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8);
+update t1 set b=2 where a=1 or b=2;
+delete from t1 where a=1 or b=2;
+drop table t1;
+
+--echo #
+--echo # End of 10.3 tests
+--echo #

sql/sql_delete.cc

@@ -371,7 +371,8 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
     DBUG_RETURN(TRUE);
 
   const_cond= (!conds || conds->const_item());
-  safe_update= MY_TEST(thd->variables.option_bits & OPTION_SAFE_UPDATES);
+  safe_update= (thd->variables.option_bits & OPTION_SAFE_UPDATES) &&
+               !thd->lex->describe;
   if (safe_update && const_cond)
   {
     my_message(ER_UPDATE_WITHOUT_KEY_IN_SAFE_MODE,
@@ -497,7 +498,7 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   }
 
   /* If running in safe sql mode, don't allow updates without keys */
-  if (table->quick_keys.is_clear_all())
+  if (!select || !select->quick)
   {
     thd->set_status_no_index_used();
     if (safe_update && !using_limit)

sql/sql_update.cc

@@ -314,7 +314,8 @@ int mysql_update(THD *thd,
                  ha_rows *found_return, ha_rows *updated_return)
 {
   bool		using_limit= limit != HA_POS_ERROR;
-  bool          safe_update= thd->variables.option_bits & OPTION_SAFE_UPDATES;
+  bool          safe_update= (thd->variables.option_bits & OPTION_SAFE_UPDATES)
+                             && !thd->lex->describe;
   bool          used_key_is_modified= FALSE, transactional_table;
   bool          will_batch= FALSE;
   bool		can_compare_record;
@@ -517,7 +518,7 @@ int mysql_update(THD *thd,
   }
 
   /* If running in safe sql mode, don't allow updates without keys */
-  if (table->quick_keys.is_clear_all())
+  if (!select || !select->quick)
   {
     thd->set_status_no_index_used();
     if (safe_update && !using_limit)