I can’t take any article like this seriously if it doesn’t lead with the #1 sql antipattern which kills performance all the time - doing things row-by-row instead of understanding that databases operate on relations, so you need to do operations over whole relations.

Very often I have seen this problem buried in code design and it always sucks. Sometimes an orm obscures this but the basic antipattern looks like

   Select some stuff
   For each row in stuff:
      … do some important things …
      Select a thing to do with this row
      … maybe do some other things …

The non-sucky version of the code above is

   Select some stuff, joining on all the things you need for the rows because databases are great
   For each row in stuff:
      … do some important things …
      … maybe do some other things …