A) (simple)

SELECT
    o.ID,
    o.Description,

    CASE o.Status
      WHEN  1  THEN 'confirmed'
      WHEN  2  THEN 'in production'
      WHEN  3  THEN 'ready'
      WHEN  4  THEN 'shipped'
      ELSE 'unknown status ''' || o.Status || ''''
    END

  FROM
    Orders o

B) (searched)

  SELECT
    o.ID,
    o.Description,

    CASE
      WHEN (o.Status IS NULL) THEN 'new'
      WHEN (o.Status =  1 ) THEN 'confirmed'
      WHEN (o.Status =  3 ) THEN 'in production'
      WHEN (o.Status =  4 ) THEN 'ready'
      WHEN (o.Status =  5 ) THEN 'shipped'
      ELSE 'unknown status ''' || o.Status || ''''
    END

  FROM
    Orders o

SELECT
           CASE o.TypeDoc 
                    WHEN  1  THEN SUM(AMOUNT) // Приход
                    WHEN  2  THEN SUM(-AMOUNT)  // Расход
           END
  FROM DOCUMENT o

SELECT
   SUM(
           CASE o.TypeDoc 
                    WHEN  1  THEN AMOUNT    // Приход
                    WHEN  2  THEN -AMOUNT   // Расход
           END
          )
  FROM DOCUMENT o