Reseting table HWM

Summary 

To gain some wasted space and improve performance at full table scans we can reset the table's HighWaterMark. We have 4 options to reorganize fragmented tables:
1. alter table move & rebuild table's indexes.
2. export / truncate / import
3. create table as select ( CTAS)
4. dbms_redefinition.
I will demonstrate all with the advantages and disadvantages and when to use each method. 

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