What does SPJ stand for in MySQL parlance?
Apparently it stands for "Select Project Join":


  What’s in a name?
  
  If some of this seems familiar but you don’t remember hearing the term
  “Adaptive Query Localization” before then you’re not going crazy –
  previous internal names were SPJ (Select Project Join) and Pushed-Down
  Joins. We just figured that Adaptive Query Localization was more
  descriptive.


Source: Dramatically Increased MySQL Cluster JOIN performance with Adaptive Query Localization