There is truth to this comment , and large amounts are written on optimising queries on DB2 databases. DB2  database design physical  supports logical database design

This comment came up today at a team meeting . It turned out the developer wrote a query assuming an index existed – and the query reflected this assumption.  It turned out the index was missing

Good physical design is important , and in most cases the DBA is responsible for either creating the physical design or signing off on the design

Physical design is a  big topic including:

-data type choice

-normalizationdenormalization

-index design

-multidimensional clustering

-partitioning

-Materialized query table

A coder can only work the existing DB2 database design : logical and physical

 Source:Jack Vamvas