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Observation: Selecting All Columns

If possible, modify the statement to select only required columns. Generally, avoid using "SELECT *" for the following reasons:

  • DB2 incurs overhead to retrieve extraneous columns.

  • "SELECT *" does not support the use of index-only retrieval.

  • A program which references a table accessed with "SELECT *" must be modified to reflect the addition or deletion of columns from the table.

  • "SELECT *" should be avoided if all the columns participate in a sort operation because of the tremendous amount of overhead that this would incur.