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Defining Join Conditions 
A join condition determines the combination of individual object records that are included in the results set.
Before an InfoSet can be activated, the join conditions have to be defined in such a way (as equal join condition) that all the available objects are connected to one another either directly or indirectly.
Usually, however, only rows containing a common InfoObject, or rows containing InfoObjects that share the same basic characteristic, are connected to one another.

Connect tables T1 and T2 using a join and set as a join condition that the F1 field from T1 must have the same value as F2 from T2. For a record from table T1, the system determines all records from T2 for which F2(T2) = F1(T1) is true. In principle, as many records from T2 can be found as required. If one or more records are found, the corresponding number of records is included in the results set, whereby the fields from T1 contain the values from that particular record in T1, and the fields from T2 contain the values of the records found in T2.
There are various ways to define join conditions:
Position the cursor over a row in an InfoObject. Press the left mouse button and, keeping the left mouse button pressed down, trace a line between this row and a row in another object. Providing that the join condition between the two rows that you have indicated is valid, the system confirms the join condition by displaying a connecting line between the two rows.
Link
Maintenance PushbuttonThe Link Maintenance dialog box appears.
In a tree structure on the left-hand side of the screen, all of the InfoProviders that are already included in the join are displayed along with their fields or attributes. If you double-click on one of these fields or attributes, the system displays on the right-hand side of the screen all of the fields or attributes with which you are able to create a join condition.
In the Selection column, set one or more of the indicators for the fields or attributes for which you want to create a join condition. The system generates valid join conditions between the fields or attributes that you specify.
You use the
Delete
Links pushbutton to undo all of the join conditions.
You use the All Characteristics or the Basic Characteristics Only pushbutton to choose between the corresponding display variants.

We recommend that you use the Basic Characteristics Only option. The All Characteristics setting displays all of the technical options involved in a join. If you are unable to find a join condition on the basic characteristic level, then the All Characteristics setting is useful, but this is an exceptional case.
When you
have finished making your settings, click on the
Continue icon.
We recommend this method because the system searches for all the possible join conditions for any field or attribute that the user specifies, ensuring that the join conditions are defined without errors.
Usually inner join operators connect all the objects in a join to one another. You can also connect objects with any of the many other objects by using a left outer join operator. This function is not available for InfoCubes.
For more information about usage and special features, see Left Outer Join.
If you want to use a left outer join operator to connect an object, select the object and choose the corresponding function from the context menu.
The system displays all of the valid join conditions that originate from this object. The connecting lines that represent these join conditions are labeled as Left Outer Join . InfoProviders that are connected using a left outer join condition are differentiated by color from those that are connected using an inner join operator.

If you use a left outer join operator to connect two objects, you have to make sure that all join conditions are linked except for these two objects with the formulation of join conditions.
Note: You cannot add an object that you have already connected by using the left outer join operator, to another object.
If you want to use an inner join operator instead of a left outer join operator, select the object that you want to connect, and choose the Inner Join option from the context menu. The system displays all the valid join conditions that originate from this object, using unlabeled connecting lines.
Once the join conditions have been defined so that they connect all the available objects to one another, either directly or indirectly, the InfoSet can be saved as active.
Choose
Check in the pushbutton toolbar to find
out if the preconditions for the activation have been met.

For objects that are joined by a left outer join operator, there is one extra condition that has to be met; all the other objects must be connected to one another either directly or indirectly.