Foreign Key RelationshipsBC030_04.1

Foreign Key Relationships

• Definition & Uses of Foreign Keys

• Prerequisites for Constructing Foreign Key Relationships

• Key Terminology

• Cardinality and Foreign Key Field Types

• Foreign Keys with Multiple Fields

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Definition of Foreign Keys

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Uses of Foreign Keys

• Maintain data integrity

• Provide help texts

• Create aggregate dictionary objects

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Prerequisites for Constructing Foreign Key Relationships• The foreign key field and the primary key of the

check table must share the same domain.

• A value table must exist for that domain.

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Check TableCheck Table

Value TableValue Table

Foreign Keys: Key Terminology

Foreign Key TableForeign Key Table

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Check Table

Value

Table

Foreign Key Terminology: Check Table = Value Table

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Foreign Key Terminology: Check Table Value Table

Check Table

Value

Table

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DataDictionary

Establishing a Foreign Key Relationship in the ABAP Dictionary

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Cardinality

n n : : m mn n : : m m1

C

1

C

N

CN

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Course Enrolment

STUDENT_ID ?

Foreign Key Field Type

• Check Table: Students

• Foreign Key Table: Course Enrolment

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Foreign Key Type: Key Fields or Key Field Candidates

Faculty Course

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Foreign Key Type: Key Fields of a Text Table

T005(Country Codes)

(T002)(Language Codes)

T005T(Country descriptions)

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Foreign Key Type: Non-Key Field Candidates

Course

Professor

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Foreign key push-button

Creating a Foreign Key Relationship

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Enter a description (short text).

Maintain cardinality n : m

Maintain foreignkey type

Check table(defaults tovalue table)

Maintaining a Foreign Key Relationship’s Attributes

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Foreign Keys with Multiple Fields

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Check TableCheck Table

Field-By-Field Assignment

Foreign Key TableForeign Key Table

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Partial Foreign Keys

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Constant Foreign Keys

“BIO”

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Generic foreign keyGeneric foreign keyGeneric foreign keyGeneric foreign key

Constant foreign keyConstant foreign keyConstant foreign keyConstant foreign key

Changing the Field Assignment