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Internal tables


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Internal tables

  1. 1. -1-Assigning Values for Complex Data ObjectsMOVE also works for copying complex tables and structures. Embedded field stringsand table components are also copied.Table TypeAn internal table is a sequence of lines with the same type. If you want to define a table type, follow the line type declaration with the addition OCCURS 0. You can also write OCCURS <n> instead of OCCURS 0, where <n> is any integer.Assigning Values Field by Field The MOVE-CORRESPONDING <rec1> to <rec2> statements transports values field by field between field strings <rec1> and <rec2>. This only works if the components have identical names. The system looks for all fields in <rec1> whose name also occurs in <rec2> and transports field <rec1>-<field name> to <rec2>-<field name> in all cases where it finds a match. All other fields remain unchanged.Internal TablesAs you have already seen, internal tables (‘arrays’ or ‘matrices’ in other terminology)are a set of lines with the same type(s). To define an internal table, simply use the addition OCCURS <n> when you declare a data object with the desired line type. The OCCURS addition turns the data object into an internal table with the same line type as that of the data object. It also determines the number of lines with which the internal table is created. Unlike the array
  2. 2. -2- concept of other programming languages, ABAP/4 can increase the number of lines in the table dynamically at runtime. If you do not know how big your internal table will be, set the OCCURS addition to 0. If you know that your internal table will be smaller than 8KB, specify the number of table lines using the OCCURS parameter. This ensures that only this amount of memory area is occupied. This is particularly important when you are working with nested structures. If the memory area is insufficient, further table lines are allocated.Working with Internal Tables In contrast with the array concepts found in other programming languages, ABAP/4 does NOT use direct access to table entries. Instead, operations on table entries are carried out using a work area. This is a temporary holding area that contains the content of the current entry for almost ALL commands dealing with the table. This work space may be either a separately defined work area or a header line that is defined when the table is defined.ABAP/4 recognizes essentially the following operations on internal tables: Command Effect Appends the contents of the work area at the end of the APPEND internal table Inserts the cumulative contents of the work area into the COLLECT internal table Inserts the contents of the work area into a particular table INSERT entry Overwrites a particular table entry with the content of the MODIFY work area DELETE Deletes a specified entry from the internal table Places the entries of an internal table in a work area one at a LOOP AT time READ Places a single internal table entry in a work area TABLE SORT Sorts the internal table
  3. 3. -3- CLEAR Deletes the work area or the internal table REFRESH Deletes the internal table FREE Releases space in memory previously occupied by tableInternal Tables With Header LineYou access internal tables record by record. You must use a work area as an interfacefor transferring data to and from the table.When you read data from an internal table, the contents of a specified table record orline overwrites the contents of the work area. Then, you can reference the contents ofthe work area in your program. When you write data to an internal table, you mustfirst enter the data in the work area from with the system can transfer the data to theinternal table. To avoid inconsistencies, it is beneficial if the work area has the same data type as the records or lines of the internal table. A safe procedure for creating work areas which are compatible with internal tables is to use the same data type for declaring both the internal table and the work area. In ABAP/4, you can distinguish between two kinds of internal tables: Internal tables WITH header lines Internal tables WITHOUT header lines A header line is similar to a work area for a database table. A work area is used as temporary storage for one entry of a database table. In a similar way, a header line is used to hold one line of an internal table. An internal table with header line is a tuple from a work area (header line) and the bulk of the table itself. Both are addressed using the same name, the interpretation of the name is context-sensitive. Hence it would
  4. 4. -4- stand for the header line in a MOVE statement, but would stand for the bulk of the table in a SEARCH statement. When you create an internal table WITH a header line, a work area is created automatically with the same data type as the rows of the internal table. The header line and the internal table have the same name. Then, the system uses this work area implicitly. In ABAP/4 statements for accessing internal tables, you can specify the work area to be used. For internal tables with header lines, you can leave out this specification. Then, the system uses the table work area implicitly.Internal Tables Without Header LineIf a table does not have a header line, you MUST provide a work area as a separaterecord to hold the content of the current entry for most commands used in processingtables. Internal tables WITHOUT a header line do NOT have a table work area declared which can be used implicitly. To access internal tables WITHOUT header lines, you must specify a work area explicitly in the corresponding ABAP/4 statements. It is a matter of your preference whether you use a header line or a work area. Remember that, for internal tables with header lines, the internal table itself and the table work areas have the same name. If you use the name in a statement, the system interprets it as the name of the table work area and NOT as the table itself. In some statement, however, you can enter square brackets after the name to address the internal table instead of the table work area as follows: <name> [ ].Declaring Internal Tables with Header LineYou define an internal table with a header line using the addition WITH HEADERLINE. A HEADER line is a work area where the currently active, individual record in the table resides.Filling Internal Tables
  5. 5. -5-The SELECT command, which you first encountered in Lesson 1, places one entryfrom a database table into the table work area of the same name in each loop pass. Ifyou want to be able to address all table entries during the program runtime, each tableentry must be saved in the internal table. You use the APPEND statement to fill the internal table: APPEND <wa> TO <itab> adds the contents of work area <wa> to the end of the internal table <itab>. If you are working with an internal table with header line, the syntax is shortened to APPEND <itab>.Array FetchYou can fill an internal table with entries from a database table using a singleSELECT statement. The database system reads the entries in bundles, not singly. Once read, the bundle is inserted en masse into the internal table. This method has performance advantages over reading in records individually via a loop. Since this is not a loop, there is no ENDSELECT. In the basic form (... INTO TABLE ...) the internal table is filled with the database entries found and existing entries are overwritten. In the variant ... APPENDING TABLE... the entries are appended to the existing entries in the internal table.Filling Internal Tables with Cumulative ValuesYou use the COLLECT statement to add the work area or header line to an existingentry of the same type or (if no such entry exists) to add it to the table as a new entry. To do this, COLLECT searches in the internal table for an entry, all of whose alphanumeric fields are identical with those of the entry in the work area or header line. If such an entry is found, COLLECT adds all numeric fields from the work area or header line to the corresponding fields in the table entry. Otherwise, the COLLECT statement appends the contents of the work area or header line to the end of the table.Sorting an Internal TableYou can sort an internal table using the SORT statement.
  6. 6. -6- If you do NOT specify any sort criteria, the table is sorted by ALLl fields except those with data type P, I and F. The fields are sorted ascending in the order in which they occur. You can use the additions BY <field name> and ASCENDING or DESCENDING to limit the sort to certain fields and determine the sort sequence and hierarchy. You should use the BY addition to narrow down the sort criteria for performance reasons. As of Release 3.0D you can perform a language-specific alphabetical sort of text fields using the TEXT addition.Using Loops with an Internal TableYou can process an internal table using the loop statement LOOP AT ... ENDLOOP.With each loop pass the system places the next table entry in the work area <wa> orthe header line of the internal table <itab>. You can restrict the entries which are read using the WHERE addition in the same way as you do when using the SELECT command. At the beginning of each loop pass, SY-TABIX is set to the value of the current table entry. When the system leaves the LOOP, SY-TABIX has the same value as it had before the loop started.Reading an Entry from an Internal TableYou use the READ TABLE <itab> statement to read a single table entry. When theentry has been read, it is in the work area <wa> or the header line of <itab>. If the entry is successfully read, the value of SY-SUBRC is zero, otherwise it is not equal to zero. SY-TABIX takes the value of the table entry read. READ TABLE <itab> INDEX <n>. The nth table entry is read. If you wish to specify individual fields as a search argument you can use the following syntax: READ TABLE <itab> WITH KEY <ki> = <v1> <k2> = <v2>...<kn> = <vn>. In this case, the first entry from <itab> is read which corresponds with the components specified in <k1>...<kn>. If the internal table is sorted by the search argument, you can use the BINARY SEARCH addition. The system then carries out a more performance-efficient binary search for the specified entry. The online documentation for the READ statement contains details of further additions.
  7. 7. -7-Changing an Internal Table I The MODIFY <itab> INDEX <i> [FROM <wa>] statement overwrites table entry ‘i’ with the contents of the work area or the header line. Entry ‘i’ must already exist. The INSERT [<wa> INTO] <itab> INDEX <i> statement creates a new table entry before entry ‘i’ containing the contents of the work area or the header line. If the table has ‘i’-1 entries, the contents of the work area or header line are appended to the internal table. The DELETE <tab> INDEX <i> statement deletes table entry ‘i’.Changing an Internal Table IIYou can make changes to an internal table from within a LOOP. The changes alwaysapply to the current table entry (SY-TABIX). INSERT A new record is inserted before the current entry containing the contents of the work area or header line. MODIFY The current entry is overwritten with the contents of the work area or header line. DELETE The current record is deleted.The following additions can be used with the DELETE statement (cf. correspondingadditions with the LOOP statement): ...WHERE <condition>. The DELETE command applies to all table entries which satisfy the condition. ...FROM <n1> TO <n2>. All entries from <n1> to <n2> inclusive are deleted. If only the FROM addition is specified, all entries from <n1> to the end of the table are deleted. If only the TO addition is specified, all entries from the beginning of the table to <n2> are deleted.Internal Table IndexThe index is the sequential number of a table line. It is NOT a table field, but iscreated and managed automatically by the system.You can use the index with the DELETE, INSERT, MODIFY, LOOP, and READstatements. In these statements, you can specify the index either as a literal or as avariable.
  8. 8. -8-After processing a particular line of an internal table, the system field SY-TABIXgenerally contains the index of that line.Deleting an Internal TableIf you are using an internal table without a header line, CLEAR <itab> deletes thebody of the table.If your internal table has a header line, CLEAR <itab> deletes the header line.If you only want to address the body of an internal table with a header line, you usethe form <itab>[]. Example 1: ITAB_WITHOUT and ITAB_WITH are two internal tables without and with header lines respectively. The command ITAB_WITHOUT = ITAB_WITH[] assigns the body of ITAB_WITH to ITAB_WITHOUT. Example 2: CLEAR ITAB_WITH[] deletes only the body of the internal table ITAB_WITH.REFRESH <itab> deletes the body of the table.Information about Internal TablesYou can get information about an internal table using the DESCRIBE TABLEstatement: The LINES addition returns the number of entries currently in the table. The OCCURS addition returns the number of OCCURS in the table definition.You can display information about any data object using the DESCRIBE FIELDstatement (see the online documentation for the DESCRIBE statement).
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