row0mysql.c:

  Allow always DROPping of a table which is only referenced by FOREIGN KEY constraints from the same table
Many files:
  Do not let REPLACE to perform internally an UPDATE if the table is referenced by a FOREIGN KEY: the manual says that REPLACE must resolve a duplicate key error semantically with DELETE(s) + INSERT, and not by an UPDATE; the internal update caused foreign key checks and cascaded operations to behave in a semantically wrong way

innobase/dict/dict0dict.c

@@ -1845,6 +1845,24 @@ dict_index_build_internal_non_clust(
 
 /*====================== FOREIGN KEY PROCESSING ========================*/
 
+/*************************************************************************
+Checks if a table is referenced by foreign keys. */
+
+ibool
+dict_table_referenced_by_foreign_key(
+/*=================================*/
+				/* out: TRUE if table is referenced by a
+				foreign key */
+	dict_table_t*	table)	/* in: InnoDB table */
+{
+	if (UT_LIST_GET_LEN(table->referenced_list) > 0) {
+		
+		return(TRUE);
+	}
+
+	return(FALSE);
+}
+
 /*************************************************************************
 Frees a foreign key struct. */
 static

innobase/include/dict0dict.h

@@ -206,6 +206,15 @@ dict_foreign_add_to_cache(
 					/* out: DB_SUCCESS or error code */
 	dict_foreign_t*	foreign);	/* in, own: foreign key constraint */
 /*************************************************************************
+Checks if a table is referenced by foreign keys. */
+
+ibool
+dict_table_referenced_by_foreign_key(
+/*=================================*/
+				/* out: TRUE if table is referenced by a
+				foreign key */
+	dict_table_t*	table);	/* in: InnoDB table */
+/*************************************************************************
 Scans a table create SQL string and adds to the data dictionary
 the foreign key constraints declared in the string. This function
 should be called after the indexes for a table have been created.

innobase/row/row0mysql.c

@@ -1997,8 +1997,15 @@ row_drop_table_for_mysql(
 		goto funct_exit;
 	}
 
+	/* Check if the table is referenced by foreign key constraints from
+	some other table (not the table itself) */
+
 	foreign = UT_LIST_GET_FIRST(table->referenced_list);
 	
+	while (foreign && foreign->foreign_table == table) {
+		foreign = UT_LIST_GET_NEXT(referenced_list, foreign);
+	}
+
 	if (foreign && trx->check_foreigns) {
 		char*	buf	= dict_foreign_err_buf;
 

sql/ha_innodb.cc

@@ -4289,7 +4289,28 @@ ha_innobase::get_foreign_key_create_info(void)
         prebuilt->trx->op_info = (char*)"";
 
   	return(str);
-}			
+}
+
+/***********************************************************************
+Checks if a table is referenced by a foreign key. The MySQL manual states that
+a REPLACE is either equivalent to an INSERT, or DELETE(s) + INSERT. Only a
+delete is then allowed internally to resolve a duplicate key conflict in
+REPLACE, not an update. */
+
+uint
+ha_innobase::referenced_by_foreign_key(void)
+/*========================================*/
+			/* out: > 0 if referenced by a FOREIGN KEY */
+{
+	row_prebuilt_t* prebuilt = (row_prebuilt_t*)innobase_prebuilt;
+
+	if (dict_table_referenced_by_foreign_key(prebuilt->table)) {
+
+		return(1);
+	}
+
+	return(0);
+}
 
 /***********************************************************************
 Frees the foreign key create info for a table stored in InnoDB, if it is

sql/ha_innodb.h

@@ -179,6 +179,7 @@ class ha_innobase: public handler
 	int check(THD* thd, HA_CHECK_OPT* check_opt);
         char* update_table_comment(const char* comment);
 	char* get_foreign_key_create_info();
+  	uint referenced_by_foreign_key();
 	void free_foreign_key_create_info(char* str);	
   	THR_LOCK_DATA **store_lock(THD *thd, THR_LOCK_DATA **to,
 			     		enum thr_lock_type lock_type);

sql/handler.h

@@ -319,6 +319,8 @@ class handler :public Sql_alloc
   virtual void append_create_info(String *packet) {}
   virtual char* get_foreign_key_create_info()
   { return(NULL);}  /* gets foreign key create string from InnoDB */
+  virtual uint referenced_by_foreign_key() { return 0;} /* used in REPLACE;
+		    is > 0 if table is referred by a FOREIGN KEY */
   virtual void init_table_handle_for_HANDLER()
   { return; }       /* prepare InnoDB for HANDLER */  
   virtual void free_foreign_key_create_info(char* str) {} 

sql/sql_insert.cc

@@ -442,7 +442,15 @@ int write_record(TABLE *table,COPY_INFO *info)
 						HA_READ_KEY_EXACT))))
 	  goto err;
       }
-      if (last_uniq_key(table,key_nr))
+      /*
+	The manual defines the REPLACE semantics that it is either an INSERT or
+	DELETE(s) + INSERT; FOREIGN KEY checks do not function in the defined
+	way if we allow MySQL to convert the latter operation internally to an
+	UPDATE.
+      */
+
+      if (last_uniq_key(table,key_nr)
+	  && !table->file->referenced_by_foreign_key())
       {
 	if ((error=table->file->update_row(table->record[1],table->record[0])))
 	  goto err;