MDEV-11842 Fail to insert on a table where a field has no default

has_no_default_value() should only fail the insert in the strict mode.

Additionally, don't check for "all fields are given values" twice,
it'll produce duplicate warnings.

mysql-test/r/trigger_no_defaults-11698.result

@@ -20,3 +20,21 @@ a	b
 10	10
 0	30
 drop table t1;
+set sql_mode=default;
+create table t1 (
+id int(11) not null auto_increment primary key,
+data1 varchar(10) not null,
+data2 varchar(10) not null
+);
+insert into t1 (data2) values ('x');
+Warnings:
+Warning	1364	Field 'data1' doesn't have a default value
+create trigger test_trigger before insert on t1 for each row begin end;
+insert into t1 (data2) values ('y');
+Warnings:
+Warning	1364	Field 'data1' doesn't have a default value
+select * from t1;
+id	data1	data2
+1		x
+2		y
+drop table t1;

mysql-test/t/trigger_no_defaults-11698.test

@@ -23,3 +23,18 @@ insert t1 (b) values (20);
 insert t1 (b) values (30);
 select * from t1;
 drop table t1;
+set sql_mode=default;
+
+#
+# MDEV-11842 Fail to insert on a table where a field has no default
+#
+create table t1 (
+  id int(11) not null auto_increment primary key,
+  data1 varchar(10) not null,
+  data2 varchar(10) not null
+);
+insert into t1 (data2) values ('x');
+create trigger test_trigger before insert on t1 for each row begin end;
+insert into t1 (data2) values ('y');
+select * from t1;
+drop table t1;

sql/sql_insert.cc

@@ -325,7 +325,7 @@ static bool has_no_default_value(THD *thd, Field *field, TABLE_LIST *table_list)
       push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN, ER_NO_DEFAULT_FOR_FIELD,
                           ER_THD(thd, ER_NO_DEFAULT_FOR_FIELD), field->field_name);
     }
-    return true;
+    return thd->really_abort_on_warning();
   }
   return false;
 }
@@ -891,7 +891,12 @@ bool mysql_insert(THD *thd,TABLE_LIST *table_list,
 
   if (fields.elements || !value_count || table_list->view != 0)
   {
-    if (check_that_all_fields_are_given_values(thd, table, table_list))
+    if (table->triggers &&
+        table->triggers->has_triggers(TRG_EVENT_INSERT, TRG_ACTION_BEFORE))
+    {
+      /* BEFORE INSERT triggers exist, the check will be done later, per row */
+    }
+    else if (check_that_all_fields_are_given_values(thd, table, table_list))
     {
       error= 1;
       goto values_loop_end;