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Lesson 3 Companion — Types, Structures & Table Operations ​

1. Why explicit table keys matter ​

Modern ABAP makes table keys part of the type. The key influences uniqueness, ordering, and lookup strategy.

text
standard → index-first general collection
sorted   → sorted key administration
hashed   → hash-key administration

2. WITH EMPTY KEY ​

For standard tables where no semantic primary key is intended, explicit WITH EMPTY KEY is clearer than relying on an implicit standard key.

3. Key reads do not automatically make a standard table fast ​

This syntax:

abap
products[ id = 'P1' ]

can still be a linear search if the table has no optimized key for id.

The expression syntax and the table's technical access characteristics are separate concerns.

4. Field symbols for in-place modification ​

abap
LOOP AT products ASSIGNING FIELD-SYMBOL(<product>).

binds the field symbol to the actual line. INTO DATA(product) creates a work-area copy.

5. In-memory CRUD terminology ​

It is fine to use CRUD as an analogy, but students should be able to say:

We changed an internal table, not persistent database data.

That distinction is critical before SQL.

6. Reference model ​

abap
TYPES:
  BEGIN OF ty_product,
    id       TYPE c LENGTH 6,
    name     TYPE string,
    category TYPE c LENGTH 10,
    price    TYPE decfloat34,
  END OF ty_product,

  tt_products TYPE HASHED TABLE OF ty_product
    WITH UNIQUE KEY id.

DATA(products) = VALUE tt_products(
  ( id = 'P00001' name = 'Keyboard' category = 'IT' price = '49.90' )
  ( id = 'P00002' name = 'Mouse' category = 'IT' price = '19.95' )
).

IF line_exists( products[ id = 'P00002' ] ).
  DATA(mouse) = products[ id = 'P00002' ].
ENDIF.

7. Missing table-expression rows ​

A direct table expression can raise CX_SY_ITAB_LINE_NOT_FOUND. The caller should only assume success when the program contract guarantees the row exists.

SAP references ​