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5.2 Internal Tables (5.2.4 Working with Internal Tables (Reading Internal…

- - - - If the nonnumeric fields match, it will not create a new row but simply adds the numeric fields of the row.
      - If the nonnumeric fields don't match, then it creates a new row.
  - - - read a single record from the internal table
    - - read more then one record
    - - use a free key
        
        can compare any field of the table
        
        the system will always perform a linear search irrespective of the type of table
    - - provide the table key
      - automatically performs a linear search for standard tables, a binary search for sorted tables, uses the hash algorithm for hashed tables
    - - If you want to use the index of the secondary key, you can explicitly specify the secondary key name via the USING KEY addition.
  - - - be used to modify a particular row of an internal table
        
        only modify the non-key fields and can't change an active key
        
        MODIFY TABLE it_sflight FROM wa_sflight.
        
        When using the key, the system scans for the corresponding record in the table and modifies it by copying the contents of the work area to the internal table.
        
        restrict the fields of the row that are modified, use the TRANSPORTING addition
        
        MODIFY TABLE it_sflight FROM wa_sflight TRANSPORTING carrid.
        
        The TRANSPORING addition transports only the specified fields from the work area to the internal table.
        
        MODIFY it_sflight FROM wa_sflight INDEX 3.
        
        When the index is provided, the corresponding row is modified by copying the contents of the work area to the internal table.
  - - - to delete all rows
- - - - hash keys must be unique
      - sorted keys can be unique or non-unique
      - DATA it_sflight TYPE STANDARD TABLE OF ty_sflight WITH NON-UNIQUE DEFAULT KEY WITH NON-UNIQUE sorted KEY by_airline COMPONENTS carrid WITH UNIQUE HASHED KEY by_flight COMPONENTS carrid connid.
        
        define the internal table lt_sflight as a standard table with a non-unique default primary key that contains two secondary keys, by_airline and by_flight.
      - an internal table can have up to 15 secondary table keys with different names
    - - WITH KEY [or WITH TABLE KEY] key_name COMPONENTS comp1...
        
        READ TABLE it_sflight INTO wa_sflight WITH TABLE KEY by_airline COMPONENTS carrid = 'AA'.
    - - use different keys and improve performance while accessing individual rows of a table
    - - For small internal tables (less than 50 rows).
      - With table that are updated or modified frequently. Each time the table is modified, the secondary key need to be updated.
      - Avoid using secondary hash keys unless you want to ensure the uniqueness of table entries.
- - - - Triggered in the first loop pass.
    - - Triggered when the value of any field up to comp in the row changes, compared to the previous record.
    - - Triggered when the value of any field up to comp in the row changes, compared to the next record.
    - - Triggered in the last loop pass.
- - - - read an individual row from an internal table into the work area
        
        READ TABLE it_sflight INTO wa_sflight WITH KEY connid='AA'.
        
        WITH KEY
        
        INDEX
        
        LOOP AT it_sflight INTO wa_sflight. ENDLOOP.
        
        FROM ... to ...
        
        WHERE
- - - - Individual rows are accessed using the table key or the row index
      - Standard table only support non-unique primary keys, which means that multiple rows in the same table can have the same key value.
      - New rows can be either appended to the end of the table using the APPEND keyword or inserted at specific positions using the INSERT keyword.
    - - New records can be inserted or appended only if they are sorted.
      - read the individual rows by index or key
      - support both unique and non-unique primary keys, defining the primary key is mandatory
    - - do not have a row index, managed using a hash algorithm
      - support only unique keys, defining the key is mandatory
    - - the any table category covers all table categories
      - the index table category only covers those table categories in which index operations are possible
      - FIELD-SYMBOLS <fs_table> TYPE ANY TABLE.
        
        Because the field symbol <fs_table> is defined as the generic type ANY TABLE, you can assign any internal table to the field symbol at runtime.