Bug#46760: Fast ALTER TABLE no longer works for InnoDB

Despite copying the value of the old table's row type
we don't always have to mark row type as being specified.
Innodb uses this to check if it can do fast ALTER TABLE
or not.
Fixed by correctly flagging the presence of row_type 
only when it's actually changed.
Added a test case for 39200.

mysql-test/r/bug46760.result

@@ -0,0 +1,43 @@
+#
+# Bug#46760: Fast ALTER TABLE no longer works for InnoDB
+#
+CREATE TABLE t1 (a INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1);
+# By using --enable_info and verifying that number of affected
+# rows is 0 we check that this ALTER TABLE is really carried
+# out as "fast/online" operation, i.e. without full-blown data
+# copying.
+#
+# I.e. info for the below statement should normally look like:
+#
+# affected rows: 0
+# info: Records: 0  Duplicates: 0  Warnings: 0
+ALTER TABLE t1 ALTER COLUMN a SET DEFAULT 10;
+affected rows: 0
+info: Records: 0  Duplicates: 0  Warnings: 0
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT '10'
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+DROP TABLE t1;
+#
+# MySQL Bug#39200: optimize table does not recognize 
+# ROW_FORMAT=COMPRESSED
+#
+CREATE TABLE t1 (a INT) ROW_FORMAT=compressed;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 ROW_FORMAT=COMPRESSED
+OPTIMIZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	optimize	status	Table is already up to date
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 ROW_FORMAT=COMPRESSED
+DROP TABLE t1;
+End of 5.1 tests

mysql-test/t/bug46760-master.opt

@@ -0,0 +1,2 @@
+--innodb-lock-wait-timeout=2
+--innodb-file-per-table

mysql-test/t/bug46760.test

@@ -0,0 +1,38 @@
+-- source include/have_innodb.inc
+
+--echo #
+--echo # Bug#46760: Fast ALTER TABLE no longer works for InnoDB
+--echo #
+
+CREATE TABLE t1 (a INT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1);
+
+--echo # By using --enable_info and verifying that number of affected
+--echo # rows is 0 we check that this ALTER TABLE is really carried
+--echo # out as "fast/online" operation, i.e. without full-blown data
+--echo # copying.
+--echo #
+--echo # I.e. info for the below statement should normally look like:
+--echo #
+--echo # affected rows: 0
+--echo # info: Records: 0  Duplicates: 0  Warnings: 0
+
+--enable_info
+ALTER TABLE t1 ALTER COLUMN a SET DEFAULT 10;
+--disable_info
+SHOW CREATE TABLE t1;
+
+DROP TABLE t1;
+
+--echo #
+--echo # MySQL Bug#39200: optimize table does not recognize 
+--echo # ROW_FORMAT=COMPRESSED
+--echo #
+
+CREATE TABLE t1 (a INT) ROW_FORMAT=compressed;
+SHOW CREATE TABLE t1;
+OPTIMIZE TABLE t1;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+--echo End of 5.1 tests

sql/handler.h

@@ -913,6 +913,15 @@ typedef struct st_ha_create_information
   ulong key_block_size;
   SQL_LIST merge_list;
   handlerton *db_type;
+  /**
+    Row type of the table definition.
+
+    Defaults to ROW_TYPE_DEFAULT for all non-ALTER statements.
+    For ALTER TABLE defaults to ROW_TYPE_NOT_USED (means "keep the current").
+
+    Can be changed either explicitly by the parser.
+    If nothing speficied inherits the value of the original table (if present).
+  */
   enum row_type row_type;
   uint null_bits;                       /* NULL bits at start of record */
   uint options;				/* OR of HA_CREATE_ options */

sql/sql_table.cc

@@ -6656,9 +6656,19 @@ view_err:
     goto err;
   }
 
+  /*
+   If this is an ALTER TABLE and no explicit row type specified reuse
+   the table's row type.
+   Note : this is the same as if the row type was specified explicitly.
+  */
   if (create_info->row_type == ROW_TYPE_NOT_USED)
   {
+    /* ALTER TABLE without explicit row type */
     create_info->row_type= table->s->row_type;
+  }
+  else
+  {
+    /* ALTER TABLE with specific row type */
     create_info->used_fields |= HA_CREATE_USED_ROW_FORMAT;
   }