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• The row from which to extract a value is determined by the order in which the rows are organized at the time that the function is executed. 

• If you are working on a randomly generated sample of your dataset, the values that you see for this function might not correspond to the values that are generated on the full dataset during job execution.
  

• If the previous value is missing or null, this function generates a missing value.
• You can use the group and order parameters to define the groups of records and the order of those records to which this function is applied. 
• This function works with the following transforms:
  • Window Transform
  • Set Transform
  • Derive Transform

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