code: func BindHint(originStmt, hintedStmt ast.StmtNode) ast.StmtNode {
  	switch x := originStmt.(type) {
  	case *ast.SelectStmt:
  		return selectBind(x, hintedStmt.(*ast.SelectStmt))
  	default:
  		return originStmt
  	}
  }
docs: // BindHint will add hints for originStmt according to hintedStmt' hints.