I’ve been looking through some code that I last worked on over a year ago. Since then several people have contributed to the project. The first thing that I noticed was a sprinkling of DISTINCT added to SELECT queries where it was originally totally unnecessary! Paul White puts it better than I could:
“
SELECT DISTINCTis sometimes an indication that someone has ‘fixed’ a query that returns duplicate rows in a naive way. This (mis-)use is probably more common among those with relatively little database experience.” https://dba.stackexchange.com/questions/139687/when-to-use-distinct
If you’re a Dev or DBA and you’re about to fix a problem by adding DISTINCT to a query, ask yourself “I am really fixing the real problem?”. And if DISTINCT is the real answer, then an equivalent GROUP BY might be more efficient.
The next thing I noticed is the addition of scalar valued functions not unsurprisingly causing less than stellar performance. An experienced DBA (and developer) should be fully aware of the performance implications of using scalar valued functions, and should avoid if possible.