Merge from mysql-5.1-innodb to mysql-5.5-innodb

storage/innobase/dict/dict0dict.c

@@ -4855,7 +4855,8 @@ void
 dict_table_replace_index_in_foreign_list(
 /*=====================================*/
 	dict_table_t*	table,  /*!< in/out: table */
-	dict_index_t*	index)	/*!< in: index to be replaced */
+	dict_index_t*	index,	/*!< in: index to be replaced */
+	const trx_t*	trx)	/*!< in: transaction handle */
 {
 	dict_foreign_t*	foreign;
 
@@ -4866,7 +4867,13 @@ dict_table_replace_index_in_foreign_list(
 		if (foreign->foreign_index == index) {
 			dict_index_t*	new_index
 				= dict_foreign_find_equiv_index(foreign);
-			ut_a(new_index);
+
+			/* There must exist an alternative index if
+			check_foreigns (FOREIGN_KEY_CHECKS) is on, 
+			since ha_innobase::prepare_drop_index had done
+			the check before we reach here. */
+
+			ut_a(new_index || !trx->check_foreigns);
 
 			foreign->foreign_index = new_index;
 		}

storage/innobase/handler/handler0alter.cc

@@ -1016,12 +1016,13 @@ ha_innobase::prepare_drop_index(
 		index->to_be_dropped = TRUE;
 	}
 
-	/* If FOREIGN_KEY_CHECK = 1 you may not drop an index defined
+	/* If FOREIGN_KEY_CHECKS = 1 you may not drop an index defined
 	for a foreign key constraint because InnoDB requires that both
-	tables contain indexes for the constraint.  Note that CREATE
-	INDEX id ON table does a CREATE INDEX and DROP INDEX, and we
-	can ignore here foreign keys because a new index for the
-	foreign key has already been created.
+	tables contain indexes for the constraint. Such index can
+	be dropped only if FOREIGN_KEY_CHECKS is set to 0.
+	Note that CREATE INDEX id ON table does a CREATE INDEX and
+	DROP INDEX, and we can ignore here foreign keys because a
+	new index for the foreign key has already been created.
 
 	We check for the foreign key constraints after marking the
 	candidate indexes for deletion, because when we check for an

storage/innobase/include/dict0dict.h

@@ -345,7 +345,8 @@ void
 dict_table_replace_index_in_foreign_list(
 /*=====================================*/
 	dict_table_t*	table,  /*!< in/out: table */
-	dict_index_t*	index);	/*!< in: index to be replaced */
+	dict_index_t*	index,	/*!< in: index to be replaced */
+	const trx_t*	trx);	/*!< in: transaction handle */
 /*********************************************************************//**
 Checks if a index is defined for a foreign key constraint. Index is a part
 of a foreign key constraint if the index is referenced by foreign key

storage/innobase/row/row0merge.c

@@ -2042,7 +2042,7 @@ row_merge_drop_index(
 	/* Replace this index with another equivalent index for all
 	foreign key constraints on this table where this index is used */
 
-	dict_table_replace_index_in_foreign_list(table, index);
+	dict_table_replace_index_in_foreign_list(table, index, trx);
 	dict_index_remove_from_cache(table, index);
 
 	trx->op_info = "";