Delete

Abstract

The delete operation terminates the validity of a given tuple. It stores the information in the database that a certain item is no longer valid. This operation can either be of physical or logical nature. A physical delete operation removes an item from the database so that it is no longer physically accessible. In contrast, a logical delete operation only terminates the validity of an item in the dataset, but keeps the tuple still available for temporal queries [Pla09]

Self Test Questions

 

• 1. Delete Implementations

  Which two possible delete implementations are mentioned in the course?

  • (a) White box and black box delete

  • (b) Physical and logical delete

  • (c) Shifted and liquid delete

  • (d) Column and row deletes

• 2. Arrays to Scan for Specific Query with Dictionary Encoding

  When applying a delete with two predicates, e.g. firstname $=$ ‘John’ AND lastname $=$ ‘Smith’, how many logical blocks in the IMDB are being looked at during determination which tuples to delete (all columns are dictionary encoded)?

  • (a) 1

  • (b) 2

  • (c) 4

  • (d) 8

• 3. Fast Delete Execution

  Assume a physical delete implementation and the following two SQL statements on our world population table:

  • (A) DELETE FROM world_population WHERE country $=$ ‘China’;

  • (B) DELETE FROM world_population WHERE country $=$ ‘Ireland’;

  Which query will execute faster? Please only consider the concepts learned so far.

  • (a) Equal execution time

  • (b) A

  • (c) Depends on the ordering of the dictionary

  • (d) B