Database Table.take and Table.drop: the hard parts

[GregoryTravis]

• Simple optimizations
  • Only calculate row_count if it’s needed
  • Simpler predicate expression for ranges where step == 1
  • Implement First/Last with LIMIT
• Allow take/drop on database tables without an ordering
• (?) Implement While by reading the table and generating a predicate column
• Implement Sample

[jdunkerley]

• Implement While by reading the table and generating a predicate column
  This should just say unsupported as predicate not a valid operation.

• Implement Sample
  This should stay unsupported for now.
  We could not allow seed control and just do a random shuffle on a GUID followed by a limit to get specified size.

[jdunkerley]

• Allow take/drop on database tables without an ordering
  ROW_NUMBER appears to allow this so this should be straight forward.

• Simple optimizations
  With exception of LAST LIMIT (which is harder these should be do-able).