sap - Can a field from primary key be used as a foreign key in the same table? - Stack Overflow
When creating a table on the application server ABAP all you have to do is to define the metadata of a table, including foreign key relationships and check tables. What are Keys? A DBMS key is an attribute or set of an attribute which helps you to identify a row(tuple) in a relation(table). They allow you to. wht is the use of primary key and foregin key and wht is different between them. Tags: abap By setting a foreign key brings a relation between two tables.
Instaed of value tables we mainly use check tables to check the field against the values in other tables.
For examples there is two tables TI and T2. One of the field values of table T1 should check against the values of the corresponding field of table T2.
In this case we mark the field of T1 as foreign key. Now the table T1 is called a foreign key table and table T2 is called as a check table.
primary and foreign keys
Following are the requirements or qualifications for assigning a foreign key relationship. The fields in check table that is used for foreign key relationship should be primary keys Both the foreign key field and check table field should have the same domain name Step by steps for creating a foreign key in a table Step 1: In the object name field enter the table name where we want to add the foreign key Step 3: Press the change button.
Point your mouse in the field which we want to make as foreign key Step 5: Enter the foreign keys button Step 6: Enter the description of foreign key Step 7: In check table filed enter the name of the check table Step 8: Enter the Yes button Step 9: Now field names of both tables will be displayed.
Press Copy button Step Check the status bar. Enter the Activate button.
You have assigned a foreign key relationship with tables In the step 8 instead of automatic assignment we can also manually specify the fields Compound Foreign Keys. A compound foreign key made up with more than one fields. Concatenated or Compound Keys Taken one step further from simple keys are concatenated or compound keys.
primary and foreign keys
As the name implies, a concatenated key is a joining of multiple single keys. Primary Keys A primary key is a key which has been chosen to be the principal or primary representative attribute for that row of data. The primary key is unique and that attribute is then used throughout the database and is accessed and passed around to other tables as the representative attribute for the data in question.
In practice, the primary key attribute is also marked as NOT NULL in most databases, meaning that attribute must always contain a value for the record to be inserted into the table. For example, imagine a User gets a new email address, which then causes all past primary key associations made using the old email address to become invalid when using the new email address.
For this reason among othersmost primary keys use a number or unique string, such as a UUID. This simply means that the database engine itself automatically assigns each new record in that table a unique primary key value that is incrementally larger than all previous values. However, most developers agree that this practice is out of date and exposes unnecessary security flaws for the system when used for some tables that represent certain data.
For example, imagine all User records are assigned an auto-incremented primary key value, know as the id attribute. If a malicious person discovers that the id attribute of a given user e.
John Smith is the valuethis exposes a bit of information already.