Inverse Distribution Functions

Inverse Distribution Functions

Defined in the SQL standard in Section 10.9 <aggregate function>, inverse distribution functions open whole new vistas both of reporting and of implementation challenges.

Vistas of Reporting

• MEDIAN! YAY!
• N-tiles (continuous and discrete)
• Many others.

Implementation Challenges

• Parser
  • Mostly done. Thanks, Atri Sharma!
  • WITHIN GROUP clause
  • Changes parser functions to work with new type of functions
  • Adds a new type for identification of ordered set functions from function lookup
  • Modifies pg_proc
  • Currently working on type coercion
  • Changes Aggref struct to identify ordered set functions.No new struct for ordered set functions since they share a lot with aggregate functions.
  • Overloaded functions support

• Planner/Optimizer
  • In progress
  • Really applies atop FILTER, not yet in master.
  • New element in ProcedureCreate
• Executor
  • New way to do aggregates: transition function now optional.
  • Directly go to final function, skipping transition functions for ordered set functions.