By Aveek Ghose, IBM India
Description Result (Y,
Comments
measure/compare program performance/runtime if program has multiple inefficient databases selects or complicated internal table
operations
Use transaction ST05 (SQL Trace) to see what indices your database accesses are using. Check these indices against your
“where” clause to assure they are significant. Check other indices for this table and where you have to change your “where” clauseto use it. Create new indices if necessary, but do not forget to
check the impact by consulting onsite coordinator.
TYPE (data element) command is used while declaring the fields whenever feasible instead of LIKE. Remember not always the data
element name matches with the table field name Internal Table is defined with “TYPE STANDARD TABLE OF” &
Work-Areas is used instead of header lines
Global variables are minimized by declaring local variables or by passing variables through parameters & arguments while creating
internal subroutine(s)
In SELECT statement, only the required fields are selected in the same order as they reside on the database table/structure/view For selecting single row from a database table, “SELECT UP to 1Rows” is used. “Select Single” is used only when full primary key
combination is known No SELECT * is used
Use “SELECT INTO TABLE” rather than “SELECT INTO CORRESPONDING FIELDS OF TABLE”
Always specify as many primary keys as possible in WHERE clause to make the Select efficient
Always select into an internal table, except when the table will be very large (i.e., when the internal table will be greater than 500,000 records). Use “Up to N Rows” when the number of
records needed is known
Select statement within a GET event is not used Wild cards like „A%‟ is avoided as much as possible Nested Select is notused instead “Inner Join” and/or “For all Entries” is used. “For all Entries” is to be used over “Loop at ITAB /
Select / ENDLOOP” (FOR ALL ENTRIES retrieves a unique result set so ensure you retrieve the full key from the database) When creating joins over database tables there should be an index at least on the inner table for the fields in the join condition
else use “ FOR ALL ENTRIES” select statement Usage of JOIN is limited to a maximum of 2 i.e. not more than 3
database tables are joined at one time
CHECK that the internal table used in FOR ALL ENTRIES is NOT empty as this will retrieve all entries from the table Delete adjacent duplicate entries from internal table before selection from database table using “ FOR ALL ENTRIES”
statement
For copying internal tables use „=‟ operator instead of Looping &
Appending
SORT inside a LOOP is not used
Sort internal table by fields in the correct order, which are used in a READ TABLE statement using BINARY SEARCH. If the order of
sorting is invalid the BINARY SEARCH will never work For large internal tables where only some rows are to be
used to set index to first relevant row before looping from that index. Use CHECK or IF…EXIT…ENDIF as appropriate to exit
from the loop
Sort fields and Sort Order on the SORT statement should be mentioned explicitly (e.g. SORT ITAB BY FLD1 FLD2
ASCENDING)
Hashed table is used for processing large amount of data (provided that you access single records only, and all with a fully
specified key)
DELETE or SORT is not used on a hashed table since it increases memory consumption
Sorted table is used for range accesses involving table key or index accesses
Fields specified in the WHERE condition with the critical operators NOT and <> (negative SQL statements) cannot be used for a search using database indexes. Whenever possible formulate
SQL statements positively
When coding IF or CASE, testing conditions are nested so that the most frequently true conditions are processed first. Also CASE isused instead of IF when testing multiple fields “equal to”
something
LOOP AT ITAB INTO WORKAREA WHERE K = „XXX‟ should be used instead of LOOP AT ITAB INTO WORKAREA / CHECK
ITAB-K = „XXX‟.
Also READ TABLE INTO WORKAREA should be used instead of only READ TABLE.
After the APPEND statement inside a loop, the work area that has been appended is cleared
Internal tables, Work areas & Global Variables are freed when no longer needed (e.g. using the FREE / REFRESH command), especially when the tables are large or the program is a batch
program
Do not delete the records of internal table inside the Loop –End loop.
Do not use: LOOP AT ITAB WHERE EQUNR = „00001011‟.
DELETE ITAB.
ENDLOOP.
Use: DELETE ITAB WHERE EQUNR = „00001011‟.
Use the MODIFY ITAB ... TRANSPORTING f1 f2 ... for single line, and MODIFY ITAB ... TRANSPORTING f1 f2 ... WHERE condition
for a set of line, to accelerate the updating of internal table
Release the locks set at the beginning
Try to avoid logical databases. If your program uses a logical database, but does not require all fields belonging to a certain GET event, always use the FIELDS addition to reduce the amount
of data selected by the logical database
Avoid the aggregate (Count, Max, Min) functions in the database selection
Use Parallel Cursor methods for nested loop into the internal tables if second internal table contains considerable number of
records
In Smartform/ Sapscript do not make redundant data retrieval where data is available in interface