There are three types cases of duplicate recordrecords: - Two or more records have identical values in each and every field (true duplicates).
- Two or more records have identical values in some fields, and the fields that do not have matching values are of no consequence (it does not matter which value we take).
- Two or more records have identical values in some fields, and one of the variable fields gives us a vale we can select on (in practice, usually a datetime field like 'last updated time').
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