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Join condition

Introduction

The join operator uses a condition that expresses which tuples from the first relation are combined (‘glued’) with which tuples from the second.
 

Examples

The example of this figure combines TitleDeed tuples with Parcel tuples, but only those for which the foreign key Plot matches with primary key PId.

Figure : The essential binary query operator: join. The join condition for this example is TitleDeed.Plot = ParcelPid, which expresses a foreign key/key link between TitleDeed and Parcel. The result relation has 3 + 3 = 6 attributes.

 

Outgoing relations

Incoming relations

  • Join is based on Join condition