SAP AND ABAP TIPS AND FACTS

Thursday, June 5, 2008

Using Logical Databases in SAP ABAP

Using Logical Databases in SAP ABAP

A logical database can be used in the following ways.

By linking it was an executable program in Program Attributes.
By using the function module LDB_PROCESS


The SELECTION SCREEN is displayed only if link the Logical Database in the Program Attributes. It is not displayed if you call it using the Function Module LDB_PROCESS.

Editing Logical Databases:

The Logical Database can be edited using the following methods.

By using the Logical Database Builder in ABAP workbench.
Transaction SE36 or SLDB the menu path is given below.

Tools---------->ABAP Work Bench--------------->Development------------->Programming Environment-------------->Logical Database Builder

Naming the Logical Database: The name can be upto 20 characters. It can also contain a three to to ten character namespace prefix, enclosed in forward slashes. From the initial screen the Logical Database can be created, copied or deleted. Before deleting the Logical Database its links form any program should be removed. You can use the where used link to find exactly where a Logical Database used before deleting it.

Posted by ABAP FRIEND at 10:21 PM
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ABAP TIPS

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ABAP TIPS

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ABAP TIPS
Always specify your conditions in the Where-clause instead of checking them yourself with check statements. The database system can then use an index (if possible) and the network load is considerably less.

ABAP TIPS
For all frequently used Select statements, try to use an index. You always use an index if you specify (a generic part of) the index fields concatenated with logical Ands in the Select statement's Where clause. Note that complex Where clauses are poison for the statement optimizer in any database system.

ABAP TIPS
If there exists at least one row of a database table or view with a certain condition, use the Select Single statement instead of a Select-Endselect-loop. Select Single requires one communication with the database system, whereas Select-Endselect needs two.

ABAP TIPS
It is always faster to use the Into Table version of a Select statement than to use Append statements.

ABAP TIPS
To read data from several logically connected tables use a join instead of nested Select statements. Network load is considerably less.

ABAP TIPS
If you want to find the maximum, minimum, sum and average value or the count of a database column, use a select list with aggregate functions instead of computing the aggregates yourself. Network load is considerably less.

ABAP TIPS
If you process your data only once, use a Select-Endselect-loop instead of collecting data in an internal table with Select Into Table. Internal table handling takes up much more space.

ABAP TIPS
Use a select list or a view instead of Select * , if you are only interested in specific columns of the table. Network load is considerably less.

ABAP TIPS
For all frequently used, read-only tables, try to use SAP buffering. Network load is considerably less.

ABAP TIPS
Whenever possible, use array operations instead of single-row operations to modify your database tables. Frequent communication between the application program and database system produces considerable overhead.

ABAP TIPS
Whenever possible, use column updates instead of single-row updates to update your database tables. Network load is considerably less.

ABAP TIPS
Instead of using nested Select loops or FOR ALL ENTRIES it is often possible to use subqueries. Network load is considerably less.

ABAP TIPS
Use the special operators CO, CA, CS, instead of programming the operations yourself. If ABAP/4 statements are executed per character on long strings, CPU consumption can rise substantially.

ABAP TIPS
Some function modules for string manipulation have become obsolete and should be replaced by ABAP/4 statements or functions: STRING_CONCATENATE... -> CONCATENATE, STRING_SPLIT... -> SPLIT, STRING_LENGTH -> strlen(), STRING_CENTER -> WRITE...TO...CENTERED, STRING_MOVE_RIGHT -> WRITE...TO...RIGHT-JUSTIFIED

ABAP TIPS
Use the CONCATENATE statement instead of programming a string concatenation of your own.

ABAP TIPS
If you want to delete the leading spaces in a string, use the ABAP/4 statement SHIFT...LEFT DELETING LEADING... .Other constructions (with CN and SHIFT...BY SY-FDPOS PLACES, with CONDENSE if possible, with CN and ASSIGN CLA+SY-FDPOS(LEN) ...) are not as fast. In any case, avoid using SHIFT inside a WHILE-loop!

ABAP TIPS
Use the SPLIT statement instead of programming a string split yourself.

ABAP TIPS
Use the strlen( ) function to restrict the DO loop to the relevant part of the field, e.g. when determinating a check-sum.

ABAP TIPS
Use "CLEAR f WITH val" whenever you want to initialize a field with a value different from the field's type-specific initial value.

ABAP TIPS
Try to keep the table ordered and use binary search or used a table of type SORTED TABLE. If TAB has n entries, linear search runs in O( n ) time, whereas binary search takes only O( log2( n ) ).

ABAP TIPS
A dynamic key access is slower than a static one, since the key specification must be evaluated at runtime. However, for large tables the costs are dominated by number of comparison needed to locate the entry.

ABAP TIPS
If you need to access an internal table with different keys repeatedly, keep your own secondary indices.With a secondary index, you can replace a linear search with a binary search plus an index access.

ABAP TIPS
LOOP ... WHERE is faster than LOOP/CHECK because LOOP ... WHERE evaluates the specified condition internally. As with any logical expressions, the performance is better if the operands of a comparison share a common type. The performance can be further enhanced if LOOP ... WHERE is combined with FROM i1 and/or TO i2, if possible.

Always use Pretty Printer and Extended Program Check before releasing the code. Do not leave unused code in the program. Comment the code thoroughly. Align the comments and the Code. Follow the SAP Standards and SAP Best Practices guidelines. It’s a good practice to take a dump of the code on your local drive.

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