Fix bug#15028 Multitable update returns different numbers of matched rows

depending on table order

multi_update::send_data() was counting updates, not updated rows. Thus if one 
record have several updates it will be counted several times in 'rows matched'
but updated only once.

multi_update::send_data() now counts only unique rows.

mysql-test/r/update.result

@@ -345,3 +345,16 @@ f1
 2000-01-01
 2002-02-02
 drop table t1;
+create table t1 (f1 int);
+create table t2 (f2 int);
+insert into t1 values(1),(2);
+insert into t2 values(1),(1);
+update t1,t2 set f1=3,f2=3 where f1=f2 and f1=1;
+affected rows: 3
+info: Rows matched: 3  Changed: 3  Warnings: 0
+update t2 set f2=1;
+update t1 set f1=1 where f1=3;
+update t2,t1 set f1=3,f2=3 where f1=f2 and f1=1;
+affected rows: 3
+info: Rows matched: 3  Changed: 3  Warnings: 0
+drop table t1,t2;

mysql-test/t/update.test

@@ -270,4 +270,21 @@ insert into t1 values('2000-01-01'),('0000-00-00');
 update t1 set f1='2002-02-02' where f1 is null;
 select * from t1;
 drop table t1;
+
+#
+# Bug#15028 Multitable update returns different numbers of matched rows
+#           depending on table order
+create table t1 (f1 int);
+create table t2 (f2 int);
+insert into t1 values(1),(2);
+insert into t2 values(1),(1);
+--enable_info
+update t1,t2 set f1=3,f2=3 where f1=f2 and f1=1;
+--disable_info
+update t2 set f2=1;
+update t1 set f1=1 where f1=3;
+--enable_info
+update t2,t1 set f1=3,f2=3 where f1=f2 and f1=1;
+--disable_info
+drop table t1,t2;
 # End of 4.1 tests

sql/sql_update.cc

@@ -1082,22 +1082,23 @@ bool multi_update::send_data(List<Item> &not_used_values)
       int error;
       TABLE *tmp_table= tmp_tables[offset];
       fill_record(tmp_table->field+1, *values_for_table[offset], 1);
-      found++;
       /* Store pointer to row */
       memcpy((char*) tmp_table->field[0]->ptr,
 	     (char*) table->file->ref, table->file->ref_length);
       /* Write row, ignoring duplicated updates to a row */
-      if ((error= tmp_table->file->write_row(tmp_table->record[0])) &&
-	  (error != HA_ERR_FOUND_DUPP_KEY &&
-	   error != HA_ERR_FOUND_DUPP_UNIQUE))
+      if (error= tmp_table->file->write_row(tmp_table->record[0]))
       {
-	if (create_myisam_from_heap(thd, tmp_table, tmp_table_param + offset,
-				    error, 1))
+        if (error != HA_ERR_FOUND_DUPP_KEY &&
+            error != HA_ERR_FOUND_DUPP_UNIQUE &&
+            create_myisam_from_heap(thd, tmp_table,
+                                         tmp_table_param + offset, error, 1))
 	{
 	  do_update=0;
 	  DBUG_RETURN(1);			// Not a table_is_full error
 	}
       }
+      else
+        found++;
     }
   }
   DBUG_RETURN(0);