-- 1. Define the source for the data
define @storelist table(id int primary key)
if (...)
  @storelist = select id from stores where store.city = @city
else if (...)
  @storelist = select @storeId
else
  @storelist = select id from stores
    
-- 2. Search for the item availability across all stores

select Availability from StoreItem where itemId = @itemId and storeId in @storelist

VD>>>def custs = linq <# from c in customers
VD>>>                    join e on in employees on c.ID == e.CustomerID
VD>>>                    select (e.FirstName, e.SurName) #>;
VD>>>def html = $<#<ul> ..$(custs; "\n"; (fName, sName) => $"<li>fName, sName</li>") </ul>#>;
VD>>>

VD>А где ты видишь тут дтали отображения? В коде используются некие абстракные коллекции customers и employees. Они скрыват те самые детали отображения. Может они — это ХМЛ.

Например, некоторые параметры не хранятся один-в-один в полях таблицы, а сериализуются в xml-ную колонку. Наличие DAL-а позволяет этот механизм хранения скрыть от бизнеса, что, имхо, очень удобно и позволяет очень просто дополнять поля сущности.

        [SqlQuery(@"
            WITH Numbered AS
            (
                SELECT TOP (@startRecord + @maxRecords)
                    ROW_NUMBER() OVER (ORDER BY fm.updt DESC) RowNum,
                    fm.mid       ID_Message,
                    fm.subj      Subject,
                    fm.uid       ID_User,
                    fm.usernick  UserNick,
                    fm.nans      AnswerCount,
                    fm.updt      UpdateTime,
                    fm.lastone   LastMessageAuthor,
                    fm.gid       ID_Forum,
                    fg.ref       ForumShortName,
                    (SELECT sum(Rating) FROM   MessageRating WHERE ID_Topic = fm.mid)  Rating,
                    (SELECT Count(*) FROM self WHERE mid = fm.mid AND (dte > COALESCE(fm.last_moderated,0))) SelfCount,
                    fm.dte       [Date]
                FROM forum_tree fm 
                INNER JOIN AllowedReadGroups(@userID,0) fg ON fg.gid = fm.gid
                WHERE fm.tid=0
                    AND ((@nans IS NULL) OR (nans = @nans))
                    AND NOT EXISTS(SELECT 1 FROM forum_filter ff WHERE ff.gid=fm.gid AND uid=@userID)
                ORDER BY fm.updt DESC
            )
            SELECT * FROM Numbered WHERE RowNum BETWEEN @startRecord + 1 AND @startRecord + @maxRecords
            OPTION (MAXDOP 1)")]
        [DataSetTable("Message")]
        public abstract ForumDataSet GetAllPublicTopics(
            int userID,
            [ParamName("nans"), ParamNullValue(-1)] int nAnswers,
            int startRecord, int maxRecords);

        public virtual ICollection GetAllPublicTopicsEx(UserInfo user, IEnumerable<int> allowed, IEnumerable<int> skip, int nAnswers, int startRecord, int maxRecords)
        {
            using (var db = RsdnDataContext.Create())
            {
                var ucread = user.IsAnonym? UserRole.User: user.UserRole;

                var result =
                    from mt in db.MessageTrees
                        join f in db.Forums on mt.ForumID equals f.ForumID
                    where
                        mt.TopicID == 0 &&
                        f.ForumID > 0 &&
                        (f.UserReadLevel >= (short)ucread || allowed.Contains(f.ForumID)) &&
                        !skip.Contains(f.ForumID)
                    orderby mt.UpdatedOn descending
                    select new
                    {
                        ID_Message        = mt.MessageID,
                        Subject           = mt.Subject,
                        ID_User           = mt.UserID,
                        UserNick          = mt.UserNick,
                        AnswerCount       = mt.AnswerNumber,
                        UpdateTime        = mt.UpdatedOn,
                        LastMessageAuthor = mt.LastAnswerBy,
                        ID_Forum          = mt.ForumID,
                        ForumShortName    = f.Alias,
                        UserRole          = f.UserReadLevel,
                        Rating            = (from mr in db.MessageRatings where mr.ID_Topic == mt.MessageID select mr.Rating).Sum()
                    };

                if (nAnswers >= 0)
                    result = from r in result where r.AnswerCount == nAnswers select r;

                result = result.Skip(startRecord).Take(maxRecords);

                return result.ToList();
            }
        }

(from o in db.Orders where ... select o).
Update(o => new Order
{
    Delayed  = true,
    Discount = o.Discount + Consts.DelayDiscountRate
});

(from o in db.Orders where ... select o).
Update(db.Orders, o => new Order
{
    Delayed  = true,
    Discount = o.Discount + Consts.DelayDiscountRate
});

V>>Не хочешь посмотреть на описание размеченных объединений в CORBA IDL и заодно посмотреть, что генерируют компиляторы на эти описания? А потом мы возьмем эти 3 примера: IDL, CLR и Хаскель, и посмотрим, что там происходит в процессе динамического определения типа.

  enum ScriptType {
    eInstallExec,
    eInstallCopy
  };
  
  union InstInfoBody switch(ScriptType) {
      case eInstallExec: CommandExecInfoBody CommandExec;
      case eInstallCopy: CopyInstallInfo CopyInstall;
    };

[Serializable, RepositoryID("IDL:EsdAgent/ScriptType:1.0"), IdlEnum]
public enum ScriptType
{
    eInstallExec,
    eInstallCopy
}

[Serializable, RepositoryID("IDL:EsdAgent/InstInfoBody:1.0"), IdlUnion]
public struct InstInfoBody : IIdlEntity, ISerializable
{
    // Fields
    private CommandExecInfoBody m_CommandExec;
    private CopyInstallInfo m_CopyInstall;
    private ScriptType m_discriminator;

    // Methods
    // приведу тело одного метода только
    public CommandExecInfoBody GetCommandExec() 
    {
        if (this.m_discriminator != ScriptType.eInstallExec)
            throw new BAD_OPERATION(0x22, CompletionStatus.Completed_MayBe);

        return this.m_CommandExec;
    }

    public CopyInstallInfo GetCopyInstall();
    public void SetCommandExec(CommandExecInfoBody val);
    public void SetCopyInstall(CopyInstallInfo val);

    // Properties
    public ScriptType Discriminator { get; }
}

    switch(instInfoBody.Discriminator) {
    case ScriptType.eInstallExec:
        CommandExecInfoBody exec = instInfoBody.GetCommandExec();
        ...
        break;
    }

if(Type1^ var1 = dynamic_cast<Type1>(obj)) { 
    // use var1 here ...
} else if (Type2^ var2 = dynamic_cast<Type2>(obj)) { ... }
} else { ... }

case obj of
    (Type1 var1) -> ...
    (_) -> case obj of 
        (Type2 var2) -> ...
        (_) -> ...

This database-related article is a stub. You can help Wikipedia by expanding it.

var managers = (from o in delayedOrders
                select manager).Distinct();
foreach(var tuple in managers.Select(m => new {m.Name, m.Email}))
{
    _notificationService.SendNotification(tuple.Email, tuple.Name, ...);
}