Core/ItemTemplate:

Rename unk0 column.
Weapons have special sounds on impact. This column is used to override these sounds by specifying another subclass. For example an item with misc subclass can sound like a stave on impact by overriding the subclass here.

sql/updates/world/2012_09_13_00_world_item_template.sql

@@ -0,0 +1 @@
+ALTER TABLE `item_template` CHANGE unk0 SoundOverrideSubclass tinyint(3) NOT NULL DEFAULT '-1';

src/server/game/DataStores/DBCStructure.h

@@ -1092,7 +1092,7 @@ struct ItemEntry
    uint32   ID;                                             // 0
    uint32   Class;                                          // 1
    uint32   SubClass;                                       // 2 some items have strange subclasses
-   int32    Unk0;                                           // 3
+   int32    SoundOverrideSubclass;                          // 3
    int32    Material;                                       // 4
    uint32   DisplayId;                                      // 5
    uint32   InventoryType;                                  // 6

src/server/game/Entities/Item/ItemPrototype.h

@@ -588,7 +588,7 @@ struct ItemTemplate
     uint32 ItemId;
     uint32 Class;                                           // id from ItemClass.dbc
     uint32 SubClass;                                        // id from ItemSubClass.dbc
-    int32  Unk0;
+    int32  SoundOverrideSubclass;                           // < 0: id from ItemSubClass.dbc, used to override weapon sound from actual SubClass
     std::string  Name1;
     uint32 DisplayInfoID;                                   // id from ItemDisplayInfo.dbc
     uint32 Quality;

src/server/game/Globals/ObjectMgr.cpp

@@ -2002,7 +2002,7 @@ void ObjectMgr::LoadItemTemplates()
     uint32 oldMSTime = getMSTime();
 
     //                                                 0      1       2               3              4        5        6       7          8         9        10        11           12
-    QueryResult result = WorldDatabase.Query("SELECT entry, class, subclass, unk0, name, displayid, Quality, Flags, FlagsExtra, BuyCount, BuyPrice, SellPrice, InventoryType, "
+    QueryResult result = WorldDatabase.Query("SELECT entry, class, subclass, SoundOverrideSubclass, name, displayid, Quality, Flags, FlagsExtra, BuyCount, BuyPrice, SellPrice, InventoryType, "
     //                                              13              14           15          16             17               18                19              20
                                              "AllowableClass, AllowableRace, ItemLevel, RequiredLevel, RequiredSkill, RequiredSkillRank, requiredspell, requiredhonorrank, "
     //                                              21                      22                       23               24        25          26             27           28
@@ -2055,7 +2055,7 @@ void ObjectMgr::LoadItemTemplates()
         itemTemplate.ItemId                    = entry;
         itemTemplate.Class                     = uint32(fields[1].GetUInt8());
         itemTemplate.SubClass                  = uint32(fields[2].GetUInt8());
-        itemTemplate.Unk0                      = fields[3].GetInt32();
+        itemTemplate.SoundOverrideSubclass     = int32(fields[3].GetInt8());
         itemTemplate.Name1                     = fields[4].GetString();
         itemTemplate.DisplayInfoID             = fields[5].GetUInt32();
         itemTemplate.Quality                   = uint32(fields[6].GetUInt8());
@@ -2171,11 +2171,11 @@ void ObjectMgr::LoadItemTemplates()
                     itemTemplate.Class = dbcitem->Class;
             }
 
-            if (itemTemplate.Unk0 != dbcitem->Unk0)
+            if (itemTemplate.SoundOverrideSubclass != dbcitem->SoundOverrideSubclass)
             {
-                sLog->outError(LOG_FILTER_SQL, "Item (Entry: %u) does not have a correct Unk0 (%i), must be %i .", entry, itemTemplate.Unk0, dbcitem->Unk0);
+                sLog->outError(LOG_FILTER_SQL, "Item (Entry: %u) does not have a correct Unk0 (%i), must be %i .", entry, itemTemplate.SoundOverrideSubclass, dbcitem->SoundOverrideSubclass);
                 if (enforceDBCAttributes)
-                    itemTemplate.Unk0 = dbcitem->Unk0;
+                    itemTemplate.SoundOverrideSubclass = dbcitem->SoundOverrideSubclass;
             }
             if (itemTemplate.Material != dbcitem->Material)
             {

src/server/game/Handlers/ItemHandler.cpp

@@ -306,7 +306,7 @@ void WorldSession::HandleItemQuerySingleOpcode(WorldPacket & recv_data)
         data << pProto->ItemId;
         data << pProto->Class;
         data << pProto->SubClass;
-        data << int32(pProto->Unk0);                        // new 2.0.3, not exist in wdb cache?
+        data << pProto->SoundOverrideSubclass;
         data << Name;
         data << uint8(0x00);                                //pProto->Name2; // blizz not send name there, just uint8(0x00); <-- \0 = empty string = empty name...
         data << uint8(0x00);                                //pProto->Name3; // blizz not send name there, just uint8(0x00);