Use of nvarchar may badly affect the performance

  • nvarchar columns should not be used unless there is a special need to store multilingual data (other than English)
  • nvarchar columns consume almost double the space compared to varchar columns, leading to increased I/O and consuming unnecessary space in buffer cache.
  • Data types should be defined consistently while using varchar/nvarchar fields as arguments for stored procedures, functions and filter conditions such that they match with data type of the column in respective base table.
  • A simple nvarchar/varchar type mismatch can have a huge performance impact because index seeks will not happen if there is data type mismatch between search variable and actual column in base table.

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