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How is it so fast (Algorithm or logic behind it)

I want to know how Oracle SQL Developer retrieves a reporting account as quickly as shown in the figure below, there is a popup that shows a list of different values ​​that are used to filter data. I am interested in knowing the method or logic used.Image

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Just thinking, he can use three approaches

  • If the column is in a unique index, it can use the index to give you unique values.
  • Otherwise, he may search for all existing entries. He should be able to make about a million per second if the data is in memory.
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