Index: frontends/php/include/graphs.inc.php
===================================================================
--- frontends/php/include/graphs.inc.php	(revision 38431)
+++ frontends/php/include/graphs.inc.php	(revision 38500)
@@ -199,18 +199,19 @@
 /**
  * Return the time of the 1st appearance of item in trends.
  *
- * @param array|int $itemids
+ * @param array $itemIds
  *
  * @return int (unixtime)
  */
-function get_min_itemclock_by_itemid($itemids) {
-	zbx_value2array($itemids);
+function get_min_itemclock_by_itemid($itemIds) {
+	zbx_value2array($itemIds);
+
 	$min = null;
 	$result = time() - SEC_PER_YEAR;
 
-	$items_by_type = array(
+	$itemTypes = array(
 		ITEM_VALUE_TYPE_FLOAT => array(),
-		ITEM_VALUE_TYPE_STR =>  array(),
+		ITEM_VALUE_TYPE_STR => array(),
 		ITEM_VALUE_TYPE_LOG => array(),
 		ITEM_VALUE_TYPE_UINT64 => array(),
 		ITEM_VALUE_TYPE_TEXT => array()
@@ -219,64 +220,68 @@
 	$dbItems = DBselect(
 		'SELECT i.itemid,i.value_type'.
 		' FROM items i'.
-		' WHERE '.dbConditionInt('i.itemid', $itemids)
+		' WHERE '.dbConditionInt('i.itemid', $itemIds)
 	);
 
 	while ($item = DBfetch($dbItems)) {
-		$items_by_type[$item['value_type']][$item['itemid']] = $item['itemid'];
+		$itemTypes[$item['value_type']][$item['itemid']] = $item['itemid'];
 	}
 
 	// data for ITEM_VALUE_TYPE_FLOAT and ITEM_VALUE_TYPE_UINT64 can be stored in trends tables or history table
 	// get max trends and history values for such type items to find out in what tables to look for data
-	$sql_from = 'history';
-	$sql_from_num = '';
+	$sqlFrom = 'history';
+	$sqlFromNum = '';
 
-	if (!empty($items_by_type[ITEM_VALUE_TYPE_FLOAT]) || !empty($items_by_type[ITEM_VALUE_TYPE_UINT64])) {
-		$itemids_numeric = zbx_array_merge($items_by_type[ITEM_VALUE_TYPE_FLOAT], $items_by_type[ITEM_VALUE_TYPE_UINT64]);
+	if (!empty($itemTypes[ITEM_VALUE_TYPE_FLOAT]) || !empty($itemTypes[ITEM_VALUE_TYPE_UINT64])) {
+		$itemIdsNumeric = zbx_array_merge($itemTypes[ITEM_VALUE_TYPE_FLOAT], $itemTypes[ITEM_VALUE_TYPE_UINT64]);
 
 		$sql = 'SELECT MAX(i.history) AS history,MAX(i.trends) AS trends'.
 				' FROM items i'.
-				' WHERE '.dbConditionInt('i.itemid', $itemids_numeric);
-		if ($table_for_numeric = DBfetch(DBselect($sql))) {
-			$sql_from_num = ($table_for_numeric['history'] > $table_for_numeric['trends']) ? 'history' : 'trends';
-			$result = time() - (SEC_PER_DAY * max($table_for_numeric['history'], $table_for_numeric['trends']));
+				' WHERE '.dbConditionInt('i.itemid', $itemIdsNumeric);
+		if ($tableForNumeric = DBfetch(DBselect($sql))) {
+			$sqlFromNum = ($tableForNumeric['history'] > $tableForNumeric['trends']) ? 'history' : 'trends';
+			$result = time() - (SEC_PER_DAY * max($tableForNumeric['history'], $tableForNumeric['trends']));
 		}
 	}
 
-	foreach ($items_by_type as $type => $items) {
+	foreach ($itemTypes as $type => $items) {
 		if (empty($items)) {
 			continue;
 		}
 
-		switch($type) {
+		switch ($type) {
 			case ITEM_VALUE_TYPE_FLOAT:
-				$sql_from = $sql_from_num;
+				$sqlFrom = $sqlFromNum;
 				break;
 			case ITEM_VALUE_TYPE_STR:
-				$sql_from = 'history_str';
+				$sqlFrom = 'history_str';
 				break;
 			case ITEM_VALUE_TYPE_LOG:
-				$sql_from = 'history_log';
+				$sqlFrom = 'history_log';
 				break;
 			case ITEM_VALUE_TYPE_UINT64:
-				$sql_from = $sql_from_num.'_uint';
+				$sqlFrom = $sqlFromNum.'_uint';
 				break;
 			case ITEM_VALUE_TYPE_TEXT:
-				$sql_from = 'history_text';
+				$sqlFrom = 'history_text';
 				break;
 			default:
-				$sql_from = 'history';
+				$sqlFrom = 'history';
 		}
 
+		foreach ($itemIds as $itemId) {
+			$sqlUnions[] = 'SELECT MIN(ht.clock) AS c FROM '.$sqlFrom.' ht WHERE ht.itemid='.$itemId;
+		}
+
 		$dbMin = DBfetch(DBselect(
-			'SELECT MIN(ht.clock) AS min_clock'.
-			' FROM '.$sql_from.' ht'.
-			' WHERE '.dbConditionInt('ht.itemid', $itemids)
+			'SELECT MIN(ht.c) AS min_clock'.
+			' FROM ('.implode(' UNION ALL ', $sqlUnions).') ht'
 		));
-		$min = empty($min) ? $dbMin['min_clock'] : min($min, $dbMin['min_clock']);
+
+		$min = $min ? min($min, $dbMin['min_clock']) : $dbMin['min_clock'];
 	}
 
-	return empty($min) ? $result : $min;
+	return $min ? $min: $result;
 }
 
 function get_graph_by_graphid($graphid) {