Difference Between Select Single and Select upto 1 row

A lot of people use the SELECT SINGLE statement to check for the existence of a value in a database.
Other people prefer to use the 'UP TO 1 ROWS' variant of the SELECT statement.

SELECT  SINGLE: 
Select single statement only selects the first record of any series of records from a database table.
That means this statement can read a single record from a database table that fulfils the 'WHERE' clause.
If this results in multiple records then only the first one will be returned and therefore may not be unique.

In below example we are fetching records of material, plant, storage location and unrestricted(quantity) from table MARD where material no is 612965 .
The database contains only 4 items for this Material no.

Example.

REPORT  ZTEST9 NO STANDARD PAGE HEADING
        LINE-SIZE 120.

TABLES: MARD.

TYPES: BEGIN OF TY_MARD,
        MATNR LIKE MARD-MATNR,
        WERKS LIKE MARD-WERKS,
        LGORT LIKE MARD-LGORT,
        LABST LIKE MARD-LABST,
      END OF TY_MARD.

DATA : WA_MARD TYPE TY_MARD.

START-OF-SELECTION.
  PERFORM GET_DATA.

*----------------------------------------------------------------------*
*       TOP-OF-PAGE
*----------------------------------------------------------------------*
TOP-OF-PAGE.

  PERFORM BUILD_PAGE_HEADER.


END-OF-SELECTION.
  PERFORM SHOW_LIST.


*&---------------------------------------------------------------------*
*&      Form  GET_DATA
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
FORM GET_DATA.
  SELECT SINGLE MATNR
        WERKS
        LGORT
        LABST FROM MARD INTO WA_MARD WHERE MATNR = '000000000000612965'.
ENDFORM.                    " GET_DATA
*&---------------------------------------------------------------------*
*&      Form  BUILD_PAGE_HEADER
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
FORM BUILD_PAGE_HEADER .
  FORMAT INTENSIFIED ON COLOR COL_HEADING.
  ULINE AT (105).
  WRITE:/ SY-VLINE,
          'Material No',
       20 SY-VLINE,
          'Plant',
       50 SY-VLINE,
          'Str.Loc',
       80 SY-VLINE,
          'Qty',
      105 SY-VLINE.
  ULINE AT (105).
  FORMAT RESET.
ENDFORM.                    " BUILD_PAGE_HEADER
*&---------------------------------------------------------------------*
*&      Form  SHOW_LIST
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
FORM SHOW_LIST .

    WRITE:/ SY-VLINE,
            WA_MARD-MATNR,
         20 SY-VLINE,
           WA_MARD-WERKS,
         50 SY-VLINE,
            WA_MARD-LGORT,
         80 SY-VLINE,
            WA_MARD-LABST,
        105 SY-VLINE.
  ULINE AT (105).


ENDFORM.                    " SHOW_LIST

output

SELECT UP TO 1 ROWS:
The 'SELECT -- UP TO 1 ROWS' statement is selects all of the relevant records that are defined by the WHERE clause,
applies any aggregate, ordering or grouping functions to them and then returns the first record of the result set.

example.
here i write same code for select up to 1 rows with order by .

REPORT  ZTEST9 NO STANDARD PAGE HEADING
        LINE-SIZE 120.

TABLES: MARD.

TYPES: BEGIN OF TY_MARD,
        MATNR LIKE MARD-MATNR,
        WERKS LIKE MARD-WERKS,
        LGORT LIKE MARD-LGORT,
        LABST LIKE MARD-LABST,
      END OF TY_MARD.

DATA : WA_MARD TYPE TY_MARD.

START-OF-SELECTION.
  PERFORM GET_DATA.

*----------------------------------------------------------------------*
*       TOP-OF-PAGE
*----------------------------------------------------------------------*
TOP-OF-PAGE.

  PERFORM BUILD_PAGE_HEADER.


END-OF-SELECTION.
  PERFORM SHOW_LIST.


*&---------------------------------------------------------------------*
*&      Form  GET_DATA
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
FORM GET_DATA.
  SELECT MATNR
                 WERKS
                 LGORT
                 LABST UP TO 1 ROWS FROM MARD INTO WA_MARD
                                   WHERE MATNR = '000000000000612965'
                                  ORDER BY WERKS DESCENDING.

   ENDSELECT.
ENDFORM.                    " GET_DATA
*&---------------------------------------------------------------------*
*&      Form  BUILD_PAGE_HEADER
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
FORM BUILD_PAGE_HEADER .
  FORMAT INTENSIFIED ON COLOR COL_HEADING.
  ULINE AT (105).
  WRITE:/ SY-VLINE,
          'Material No',
       20 SY-VLINE,
          'Plant',
       50 SY-VLINE,
          'Str.Loc',
       80 SY-VLINE,
          'Qty',
      105 SY-VLINE.
  ULINE AT (105).
  FORMAT RESET.
ENDFORM.                    " BUILD_PAGE_HEADER
*&---------------------------------------------------------------------*
*&      Form  SHOW_LIST
*&---------------------------------------------------------------------*
*       text
*----------------------------------------------------------------------*
FORM SHOW_LIST .

    WRITE:/ SY-VLINE,
            WA_MARD-MATNR,
         20 SY-VLINE,
           WA_MARD-WERKS,
         50 SY-VLINE,
            WA_MARD-LGORT,
         80 SY-VLINE,
            WA_MARD-LABST,
        105 SY-VLINE.
  ULINE AT (105).


ENDFORM.                    " SHOW_LIST

output