decster commented on issue #3469:
URL: 
https://github.com/apache/incubator-doris/issues/3469#issuecomment-643032202


   > Does the "memory engine table" has primary key columns?
   
   Yes, to support update/delete every row should have a primary key. This is 
equivalent to:
   
   Agg table with agg key as primary key
   Uniq table with uniq key as primary key
   Even for the duplicate table,  a hidden seq id column is required to 
identify updates belonging to which row.
   
   So a update like:
   
   ```
   update t set col1 = col1+1 where xxx;
   ```
   
   first scan rows with seqid and col1 and filter xxx, and then construct a 
writetxn with primary key and updated col1.
   


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