Информация это сведения об объектах и явлениях окружающей среды, их параметрах, свойствах и состояниях, которые уменьшают имеющуюся о них степень неопределенности, неполноты знаний

Дополнительные возможности языка SQL

Представления (VIEW)

Хранимые процедуры

Триггеры

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  prevent changes (e.g. prevent an invoice from being changed after it's been mailed out)
  
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  log changes (e.g. keep a copy of the old data)
  
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  audit changes (e.g. keep a log of the users and roles involved in changes)
  
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  enhance changes (e.g. ensure that every change to a record is time-stamped by the server's clock, not the client's)
  
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  enforce business rules (e.g. require that every invoice have at least one line item)
  
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  execute business rules (e.g. notify a manager every time an employee's bank account number changes)
  
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  replicate data (e.g. store a record of every change, to be shipped to another database later)
  
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  enhance performance (e.g. update the account balance after every detail transaction, for faster queries)
  

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  do not accept parameters or arguments (but may store affected-data in temporary tables)
  
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  cannot perform commit or rollback operations because they are part of the triggering SQL statement (only through autonomous transactions)
  
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  can cancel a requested operation
  
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  can cause mutating table errors, if they are poorly written.