Bug#48525: trigger changes "Column 'id' cannot be null" behaviour

CHECK_FIELD_IGNORE was treated as CHECK_FIELD_ERROR_FOR_NULL;
UPDATE...SET...NULL on NOT NULL fields behaved differently after
a trigger.

Now distinguishes between IGNORE and ERROR_FOR_NULL and save/restores
check-field options.

mysql-test/r/trigger.result:
  Show that UPDATE...SET...NULL on NOT NULL columns doesn't behave differently
  when run after a trigger.
mysql-test/t/trigger.test:
  Show that UPDATE...SET...NULL on NOT NULL columns doesn't behave differently
  when run after a trigger.
sql/field_conv.cc:
  CHECK_FIELD_IGNORE was treated as CHECK_FIELD_ERROR_FOR_NULL.
  Distinguish between the two.
sql/sp_head.cc:
  raise error as needed
sql/sql_class.cc:
  Save and restore check-fields options.
sql/sql_class.h:
  Make room so we can save check-fields options.
sql/sql_insert.cc:
  raise error as needed

1 files changed, 13 insertions, 0 deletions

diff --git a/mysql-test/t/trigger.test b/mysql-test/t/trigger.test
index 1e55f9d5993..db41a12a9ac 100644
--- a/mysql-test/t/trigger.test
+++ b/mysql-test/t/trigger.test
@@ -2396,4 +2396,17 @@ SELECT * FROM t2;
 
 DROP TABLE t1, t2;
 
+#
+# Bug #48525: trigger changes "Column 'id' cannot be null" behaviour
+#
+CREATE TABLE t1 (id INT NOT NULL);
+CREATE TABLE t2 (id INT NOT NULL);
+INSERT t1 VALUES (1),(2),(3);
+UPDATE t1 SET id=NULL;
+CREATE TRIGGER t1_bu BEFORE UPDATE ON t1 FOR EACH ROW
+  INSERT INTO t2 VALUES (3);
+UPDATE t1 SET id=NULL;
+DROP TRIGGER t1_bu;
+DROP TABLE t1,t2;
+
 --echo End of 5.1 tests.