MDEV-7817 ALTER TABLE {ADD|DROP} INDEX IF [NOT] EXISTS does not get written...

MDEV-7817 ALTER TABLE {ADD|DROP} INDEX IF [NOT] EXISTS does not get written into binlog if nothing to do.
Just log the ALTER statement even if there's nothing to do.

mysql-test/r/create_drop_binlog.result

@@ -345,3 +345,48 @@ RESET MASTER;
 SHOW MASTER STATUS;
 File	Position	Binlog_Do_DB	Binlog_Ignore_DB
 master-bin.000001	<pos>		
+CREATE TABLE t1(a INT, b INT);
+CREATE TABLE IF NOT EXISTS t1(a INT, b INT);
+Warnings:
+Note	1050	Table 't1' already exists
+CREATE INDEX IF NOT EXISTS i1 ON t1(a);
+CREATE INDEX IF NOT EXISTS i1 ON t1(a);
+Warnings:
+Note	1061	Duplicate key name 'i1'
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) DEFAULT NULL,
+  KEY `i1` (`a`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP INDEX IF EXISTS i1 ON t1;
+DROP INDEX IF EXISTS i1 ON t1;
+Warnings:
+Note	1091	Can't DROP 'i1'; check that column/key exists
+DROP TABLE t1;
+DROP TABLE IF EXISTS t1;
+Warnings:
+Note	1051	Unknown table 'test.t1'
+SHOW BINLOG EVENTS;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+#	#	Format_desc	1	#	VER
+#	#	Gtid_list	1	#	[]
+#	#	Binlog_checkpoint	1	#	master-bin.000001
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; CREATE TABLE t1(a INT, b INT)
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; CREATE TABLE IF NOT EXISTS t1(a INT, b INT)
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; CREATE INDEX IF NOT EXISTS i1 ON t1(a)
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; CREATE INDEX IF NOT EXISTS i1 ON t1(a)
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; DROP INDEX IF EXISTS i1 ON t1
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; DROP INDEX IF EXISTS i1 ON t1
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; DROP TABLE `t1` /* generated by server */
+#	#	Gtid	1	#	GTID #-#-#
+#	#	Query	1	#	use `test`; DROP TABLE IF EXISTS `t1` /* generated by server */
+RESET MASTER;

mysql-test/t/create_drop_binlog.test

@@ -175,3 +175,22 @@ SHOW MASTER STATUS;
 RESET MASTER;
 --replace_result $pos <pos>
 SHOW MASTER STATUS;
+
+#
+# mdev-7817 ALTER TABLE {ADD|DROP} INDEX IF [NOT] EXISTS does not get written into binlog if nothing to do
+# 
+
+CREATE TABLE t1(a INT, b INT);
+CREATE TABLE IF NOT EXISTS t1(a INT, b INT);
+CREATE INDEX IF NOT EXISTS i1 ON t1(a);
+CREATE INDEX IF NOT EXISTS i1 ON t1(a);
+SHOW CREATE TABLE t1;
+DROP INDEX IF EXISTS i1 ON t1;
+DROP INDEX IF EXISTS i1 ON t1;
+DROP TABLE t1;
+DROP TABLE IF EXISTS t1;
+--replace_column 1 # 2 # 5 #
+--replace_regex /xid=[0-9]+/xid=XX/ /GTID [0-9]+-[0-9]+-[0-9]+/GTID #-#-#/ /Server.ver.*/VER/
+SHOW BINLOG EVENTS;
+RESET MASTER;
+

sql/sql_table.cc

@@ -8484,6 +8484,10 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
                 ER_THD(thd, ER_INSERT_INFO), 0L, 0L,
                 thd->get_stmt_da()->current_statement_warn_count());
     my_ok(thd, 0L, 0L, alter_ctx.tmp_name);
+
+    if (write_bin_log(thd, true, thd->query(), thd->query_length()))
+      DBUG_RETURN(true);
+
     DBUG_RETURN(false);
   }