Refactor SQL(), Pos(), End()

[apstndb]

After introducing helper functions of SQL(), Pos(), End(), there are mixed style implementation of their functions.

It is better to refactoring existing functions, but they are not yet done.
#120 (comment)

• Rewrite SQL() Refactor SQL() methods #173
• Rewrite Pos(), End()
  • It is resolved by Generate ast/pos.go automatically #174

[apstndb]

Close as completed