8. Joins in Qlik Sense

Introduction

This tutorial explores the different types of joins in Qlik Sense, focusing on their evaluation and practical application. Understanding joins is crucial for data modeling and analysis, as they determine how data from different tables interacts. This guide will walk you through the four main types of joins used in Qlik Sense and how to implement them effectively.

Step 1: Understanding Joins in Qlik Sense

Joins are used to combine data from multiple tables based on common fields. In Qlik Sense, there are four primary types of joins:

• Inner Join: Combines records that have matching values in both tables.
• Outer Join: Includes all records from one table and the matched records from the second table. It can be further categorized into:
  • Left Join: All records from the left table and matched records from the right.
  • Right Join: All records from the right table and matched records from the left.
• Full Outer Join: Combines all records from both tables, filling in gaps with nulls where there are no matches.
• Concat Join: Combines tables vertically by appending rows from one table to another.

Step 2: Implementing Inner Joins

To create an inner join in Qlik Sense:

1. Load the data from the first table.
2. Load the data from the second table using the following syntax:

   INNER JOIN (Table1)
   LOAD
       Field1,
       Field2
   FROM [DataSource2];
   

3. Review the results to ensure only matching records from both tables appear.

Practical Tip

Use inner joins when you only need records that exist in both datasets. This is useful for filtering out irrelevant data.

Step 3: Implementing Left Joins

To create a left join:

1. Load the first table.
2. Load the second table with the left join syntax:

   LEFT JOIN (Table1)
   LOAD
       Field1,
       Field2
   FROM [DataSource2];
   

3. Verify that all records from the left table are retained, with nulls for unmatched records from the right table.

Common Pitfall

Be cautious of duplicate field names across tables. Rename fields in the load statement if necessary to avoid confusion.

Step 4: Implementing Right Joins

For a right join:

1. Load the first table.
2. Load the second table using right join syntax:

   RIGHT JOIN (Table1)
   LOAD
       Field1,
       Field2
   FROM [DataSource2];
   

3. Check that all records from the right table are included, with nulls for unmatched records from the left.

Practical Tip

Right joins can be particularly useful when the right table contains the primary data you need, while the left table provides additional context.

Step 5: Implementing Full Outer Joins

To perform a full outer join:

1. Load both tables.
2. Use the following syntax for the join:

   FULL OUTER JOIN (Table1)
   LOAD
       Field1,
       Field2
   FROM [DataSource2];
   

3. Ensure that all records from both tables are combined, with nulls filled in for missing matches.

Important Note

Full outer joins can result in a larger dataset. Use them judiciously to avoid performance issues.

Step 6: Using Concat Joins

To create a concat join:

1. Load the first table.
2. Use the following syntax to append the second table:

   CONCATENATE (Table1)
   LOAD
       Field1,
       Field2
   FROM [DataSource2];
   

3. Confirm that the data from both tables is combined vertically.

Best Practice

Use concat joins when the two tables share the same structure, allowing for a seamless combination of records.

Conclusion

Understanding and applying the various types of joins in Qlik Sense is essential for effective data analysis. Each join type serves a specific purpose, from filtering to combining datasets. Experiment with these joins in your projects to see how they can enhance your data modeling. Consider reviewing additional resources or tutorials on advanced Qlik Sense techniques to further your skills.