MDEV-18732 InnoDB: ALTER IGNORE returns error for NULL

Only starting with MariaDB 10.3.8 (MDEV-16365), InnoDB can actually
handle ALTER IGNORE TABLE correctly when introducing a NOT NULL
attribute to a column that contains a NULL value. Between
MariaDB Server 10.0 and 10.2, we would incorrectly return an error
for ALTER IGNORE TABLE when the column contains a NULL value.

mysql-test/suite/innodb/r/innodb-alter-nullable.result

@@ -55,3 +55,37 @@ CREATE TABLE t1(c1 INT) ENGINE=InnoDB;
 ALTER TABLE t1 ADD CONSTRAINT UNIQUE KEY i1(c1);
 ALTER TABLE t1 CHANGE c1 c1 INT NOT NULL,ADD KEY(c1);
 DROP TABLE t1;
+#
+# MDEV-18732 InnoDB: ALTER IGNORE returns error for NULL
+#
+SET @mode = @@sql_mode;
+SET sql_mode = STRICT_TRANS_TABLES;
+CREATE TABLE t1(c INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (NULL);
+ALTER IGNORE TABLE t1 MODIFY c INT NOT NULL;
+affected rows: 1
+info: Records: 1  Duplicates: 0  Warnings: 1
+Warnings:
+Warning	1265	Data truncated for column 'c' at row 1
+INSERT INTO t1 VALUES (NULL);
+ERROR 23000: Column 'c' cannot be null
+SELECT * FROM t1;
+c
+0
+DROP TABLE t1;
+CREATE TABLE t1(c INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (NULL),(1),(1);
+ALTER IGNORE TABLE t1 ADD UNIQUE(c);
+affected rows: 3
+info: Records: 3  Duplicates: 1  Warnings: 0
+ALTER IGNORE TABLE t1 ADD PRIMARY KEY(c);
+affected rows: 2
+info: Records: 2  Duplicates: 0  Warnings: 1
+Warnings:
+Warning	1265	Data truncated for column 'c' at row 1
+SELECT * FROM t1;
+c
+0
+1
+DROP TABLE t1;
+SET sql_mode = @mode;

mysql-test/suite/innodb/t/innodb-alter-nullable.test

@@ -76,6 +76,32 @@ ALTER TABLE t1 ADD CONSTRAINT UNIQUE KEY i1(c1);
 ALTER TABLE t1 CHANGE c1 c1 INT NOT NULL,ADD KEY(c1);
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-18732 InnoDB: ALTER IGNORE returns error for NULL
+--echo #
+
+SET @mode = @@sql_mode;
+SET sql_mode = STRICT_TRANS_TABLES;
+CREATE TABLE t1(c INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (NULL);
+--enable_info
+ALTER IGNORE TABLE t1 MODIFY c INT NOT NULL;
+--disable_info
+--error ER_BAD_NULL_ERROR
+INSERT INTO t1 VALUES (NULL);
+SELECT * FROM t1;
+DROP TABLE t1;
+
+CREATE TABLE t1(c INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (NULL),(1),(1);
+--enable_info
+ALTER IGNORE TABLE t1 ADD UNIQUE(c);
+ALTER IGNORE TABLE t1 ADD PRIMARY KEY(c);
+--disable_info
+SELECT * FROM t1;
+DROP TABLE t1;
+SET sql_mode = @mode;
+
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.
 --source include/wait_until_count_sessions.inc

storage/innobase/handler/handler0alter.cc

@@ -328,7 +328,7 @@ ha_innobase::check_if_supported_inplace_alter(
 	NULL to a NOT NULL value. */
 	if ((ha_alter_info->handler_flags
 	     & Alter_inplace_info::ALTER_COLUMN_NOT_NULLABLE)
-	    && !thd_is_strict_mode(user_thd)) {
+	    && (ha_alter_info->ignore || !thd_is_strict_mode(user_thd))) {
 		ha_alter_info->unsupported_reason = innobase_get_err_msg(
 			ER_ALTER_OPERATION_NOT_SUPPORTED_REASON_NOT_NULL);
 		DBUG_RETURN(HA_ALTER_INPLACE_NOT_SUPPORTED);

storage/xtradb/handler/handler0alter.cc

@@ -332,7 +332,7 @@ ha_innobase::check_if_supported_inplace_alter(
 	NULL to a NOT NULL value. */
 	if ((ha_alter_info->handler_flags
 	     & Alter_inplace_info::ALTER_COLUMN_NOT_NULLABLE)
-	    && !thd_is_strict_mode(user_thd)) {
+	    && (ha_alter_info->ignore || !thd_is_strict_mode(user_thd))) {
 		ha_alter_info->unsupported_reason = innobase_get_err_msg(
 			ER_ALTER_OPERATION_NOT_SUPPORTED_REASON_NOT_NULL);
 		DBUG_RETURN(HA_ALTER_INPLACE_NOT_SUPPORTED);