Bug#37337527 >= 8.0.27 Error 1048 when updating row with empty_sql mode

An UPDATE following an INSERT on tables with before insert trigger
can sometime fail with null value error if the INSERT had added a null
value to non-null column. This happens when null values are inserted
into non-null fields under allowed sql_mode.

The before insert trigger sets tmp_null flag for the non-null field
indicating the temporary null status as part of the insert. This flag
is not reset at the end of trigger processing and used during the
subsequent UPDATE command. This unexpected null flag is causing
the update to fail with null-value error even though the update is
not handling any null.

Fix: Reset the tmp_null flag at the end of insert trigger flow processing.

Change-Id: If9524a7aee17130ee53becbe47229f50bdbc49d2

Author: Ajo Robert

mysql-test/r/trigger.result

@@ -3417,3 +3417,18 @@ Trigger	sql_mode	SQL Original Statement	character_set_client	collation_connectio
 DROP TRIGGER очень_очень_очень_очень_очень_очень_очень_очень_длинная_строка_é;
 DROP TABLE t1;
 SET NAMES default;
+#
+# Bug#37337527 >= 8.0.27 Error 1048 when updating row with empty_sql mode
+#
+CREATE TABLE t1 (c1 INT, c2 INT NOT NULL);
+CREATE TRIGGER t_t1 BEFORE INSERT ON t1 FOR EACH ROW BEGIN END;
+SET SESSION sql_mode = '';
+INSERT INTO t1(c1) VALUES (1);
+Warnings:
+Warning	1364	Field 'c2' doesn't have a default value
+SELECT * FROM t1;
+c1	c2
+1	0
+UPDATE t1 SET c2=3 WHERE c1=1;
+DROP TABLE t1;
+SET sql_mode=default;

mysql-test/t/trigger.test

@@ -4109,3 +4109,16 @@ DROP TRIGGER очень_очень_очень_очень_очень_очень_
 
 DROP TABLE t1;
 SET NAMES default;
+
+--echo #
+--echo # Bug#37337527 >= 8.0.27 Error 1048 when updating row with empty_sql mode
+--echo #
+CREATE TABLE t1 (c1 INT, c2 INT NOT NULL);
+CREATE TRIGGER t_t1 BEFORE INSERT ON t1 FOR EACH ROW BEGIN END;
+
+SET SESSION sql_mode = '';
+INSERT INTO t1(c1) VALUES (1);
+SELECT * FROM t1;
+UPDATE t1 SET c2=3 WHERE c1=1;
+DROP TABLE t1;
+SET sql_mode=default;

sql/sql_base.cc

@@ -9880,8 +9880,10 @@ bool fill_record_n_invoke_before_triggers(
     }
 
     table->triggers->disable_fields_temporary_nullability();
+    rc = rc || check_inserting_record(thd, table->field);
+    table->triggers->reset_field_nulls();
 
-    return rc || check_inserting_record(thd, table->field);
+    return rc;
   } else {
     if (fill_record(thd, table, fields, values, nullptr, nullptr,
                     raise_autoinc_has_expl_non_null_val))

sql/table_trigger_dispatcher.cc

@@ -639,6 +639,16 @@ void Table_trigger_dispatcher::disable_fields_temporary_nullability() {
     (*next_field)->reset_tmp_nullable();
 }
 
+/**
+  Reset the temporary null values set to the field for triggers.
+ */
+void Table_trigger_dispatcher::reset_field_nulls() {
+  assert(m_subject_table);
+
+  for (Field **next_field = m_subject_table->field; *next_field; ++next_field)
+    (*next_field)->reset_tmp_null();
+}
+
 /**
   Iterate along triggers and print necessary upgrade warnings.
 

sql/table_trigger_dispatcher.h

@@ -161,6 +161,7 @@ class Table_trigger_dispatcher : public Table_trigger_field_support {
 
   void enable_fields_temporary_nullability(THD *thd);
   void disable_fields_temporary_nullability();
+  void reset_field_nulls();
 
   void print_upgrade_warnings(THD *thd);