1 files changed, 74 insertions, 2 deletions
diff --git a/sql/key.cc b/sql/key.cc
index a2c3b2c8989..9425a368669 100644
--- a/sql/key.cc
+++ b/sql/key.cc
@@ -156,9 +156,28 @@ void key_restore(TABLE *table,byte *key,uint idx,uint key_length)
 } /* key_restore */
 
 
-	/* Compare if a key has changed */
+/*
+  Compare if a key has changed
+
+  SYNOPSIS
+    key_cmp_if_same()
+    table		TABLE
+    key			key to compare to row
+    idx			Index used
+    key_length		Length of key
+
+  NOTES
+    In theory we could just call field->cmp() for all field types,
+    but as we are only interested if a key has changed (not if the key is
+    larger or smaller than the previous value) we can do things a bit
+    faster by using memcmp() instead.
+
+  RETURN
+    0	If key is equal
+    1	Key has changed
+*/
 
-int key_cmp(TABLE *table,const byte *key,uint idx,uint key_length)
+bool key_cmp_if_same(TABLE *table,const byte *key,uint idx,uint key_length)
 {
   uint length;
   KEY_PART_INFO *key_part;
@@ -281,3 +300,56 @@ bool check_if_key_used(TABLE *table, uint idx, List<Item> &fields)
     return check_if_key_used(table, table->primary_key, fields);
   return 0;
 }
+
+
+/*
+  Compare key in row to a given key
+
+  SYNOPSIS
+    key_cmp()
+    key_part		Key part handler
+    key			Key to compare to value in table->record[0]
+    key_length		length of 'key'
+
+  RETURN
+    The return value is SIGN(key_in_row - range_key):
+
+    0			Key is equal to range or 'range' == 0 (no range)
+   -1			Key is less than range
+    1			Key is larger than range
+*/
+
+int key_cmp(KEY_PART_INFO *key_part, const byte *key, uint key_length)
+{
+  uint store_length;
+
+  for (const byte *end=key + key_length;
+       key < end;
+       key+= store_length, key_part++)
+  {
+    int cmp;
+    store_length= key_part->store_length;
+    if (key_part->null_bit)
+    {
+      /* This key part allows null values; NULL is lower than everything */
+      register bool field_is_null= key_part->field->is_null();
+      if (*key)                                 // If range key is null
+      {
+	/* the range is expecting a null value */
+	if (!field_is_null)
+	  return 1;                             // Found key is > range
+        /* null -- exact match, go to next key part */
+	continue;
+      }
+      else if (field_is_null)
+	return -1;                              // NULL is less than any value
+      key++;					// Skip null byte
+      store_length--;
+    }
+    if ((cmp=key_part->field->key_cmp((byte*) key, key_part->length)) < 0)
+      return -1;
+    if (cmp > 0)
+      return 1;
+  }
+  return 0;                                     // Keys are equal
+}