Explain the different types of joins in SAP HANA?
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Explain the different types of joins in SAP HANA?
Answer
Sap-Analyst (2015-present)
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The types of joins in SAP HANA divides into two categories; Standard database joins and Specific joins.
1. Standard Database Joins
Inner join: The inner join joins the left and right tables with only matching records. That is, only that part in both tables that coincides displays. Inner joins are very useful while creating information models as we can use it to join tables in attribute views.
Left outer join: The left outer join combines the entire left table with only the matching records from the right table. If some the engine can’t find any records matching for the left columns in the right table then it returns NULL at those places.
Right outer join: The right outer join combines the entire right table with the matching contents in the left table. We rarely use the right outer join in real scenarios. It returns NULL in place of values which do not find an association with the records in the right table.
Full outer join/Union: A full outer join combines all the records from both left and right tables irrespective of the matching conditions. The cells which are not able to find any association with the other table are left NULL.
2. SAP HANA Specific Joins
Referential join: Referential joins are like inner joins but with a condition of keeping the referential integrity intact.
We use it whenever there is a primary key and foreign key association between two tables. And, referential integrity is when for every value in the foreign key column, there is a reference value in the primary key column of the master data table.
From a performance point of view, referential joins are better than inner joins. Referential joins are necessary for star schemas as long as referential integrity maintains.
Text join: Text join provides a description of text records in the language specific to the user. If user A selects the language as German, then all the details regarding the table and columns will display to the user in German. We use text joins for joining a text table with a master data table.
Note: This one is the favorite SAP HANA interview question of most interviewees.
