Chapter 03_Foreign Key Relationships

8/10/2019 Chapter 03_Foreign Key Relationships

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IBM Global Business Services

IBM Corporation 2013Foreign Key Relationships Dec-2008

Foreign Key Relationships


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IBM Corporation 20132 Dec-2008Foreign Key Relationships |

Objectives

The participants will be able to:

Define and Use Foreign Keys

Understand the Prerequisites for Constructing Foreign Key Relationships

Interpret Cardinality and Foreign Key Field Types

Create Foreign Key Relation


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Definition of Foreign Keys

Relationships between tables are represented in the ABAP Dictionary byforeign keys.

A foreign key is a field (or combination of fields) that represents the primary

key of another table.


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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 samedomain.


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Check Table

Value Table

Foreign Keys: Key Terminology

Foreign Key Table

The table containing the set of

allowed values attached to a domain

The table that is referenced by a foreign

key

The table containing fields that are

the primary key of the other table


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CheckTable ValueTable

Foreign Key Terminology: Check Table = Value Table

In many cases, the value table and the check table will be the same


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Foreign Key Terminology: Check Table Value Table

Check

Table

Value

Table

Sometimes check table is another table containing a subset of the records ina value table.


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Establishing a Foreign Key Relationship in the ABAPDictionary

During defining Foreign Key Relationship, system suggests a Foreign KeyRelationship for you.


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Cardinality

n : m

1

C

1

C

N

CN

When creating foreign key relationships, you should always specify the cardinalityof that relationship


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Creating a Foreign Key Relationship

Foreign key push-button


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Maintaining a Foreign Key Relationships Attributes

Enter a description (short text).

Maintain foreign

key type

Maintain cardinality n : m

Check table


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If the primary key of a check table has multiple fields (i.e. it has a compositeprimary key), some type of assignment must be made for each field when

creating a foreign key relationship.

Foreign Keys with Multiple Fields


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Check Table

Field-By-Field Assignment

Foreign Key Table

When performing a field-by-field assignment, all key fields in the check tableare used to determine valid entries in the foreign key table.


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Partial Foreign Keys

When creating a partial foreign key, certain fields are flagged as generic.

These fields are ignored by the system when validating records that are inserted

into the foreign key table.


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Constant Foreign Keys

When creating a constant foreign key, certain fields are assigned a literal value

Only records in the check table with that value in the corresponding field are

used to determine whether records in the foreign key table are valid.


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Combined use of Partial and Constant foreign keys

Generic foreign key

Constant foreign key


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Demonstration

Creation of a new transparent table for holding the payroll data for employees inan organization and establish a foreign key relationship with the employee table

created for the previous chapter.


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Practice

Creation of a new transparent table for holding the payroll data for employees inan organization and establish a foreign key relationship with the employee table

created for the previous chapter.

IBM Gl b l B i S i


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Summary

Relationships between tables are represented in the ABAP Dictionary by foreignkeys. A foreign key is a field (or combination of fields) that represents the primary

key of another table.

Foreign keys maintain data integrity & provide help texts.

In order to establish a foreign key relationship in SAP, the fields involved must

share the same domain.

IBM Gl b l B i S i


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Questions

What is a foreign key ? What is the need to define a foreign key relationship ?

What is meant by cardinality in a foreign key relationship ?

Documents

Chapter 03_Foreign Key Relationships