PostgreSQL FULL JOIN – Combining All Data from Two Tables

Welcome to The Coding College, your one-stop resource for mastering coding and database concepts! In this tutorial, we’ll cover the FULL JOIN in PostgreSQL, which combines rows from two tables, including unmatched rows from both sides.

What is a FULL JOIN?

The FULL JOIN in PostgreSQL combines the result of a LEFT JOIN and a RIGHT JOIN. It includes all rows from both tables:

• Matching rows are joined.
• Non-matching rows are included with NULL values for columns from the other table.

Syntax

SELECT column_name(s)
FROM table1
FULL JOIN table2
ON table1.column_name = table2.column_name;

• table1: The first table.
• table2: The second table.
• ON: Specifies the condition for joining rows.

Example: Sample Tables

Table 1: students

Table 2: courses

Example 1: Basic FULL JOIN

SELECT s.name, s.course_id, c.course_name
FROM students AS s
FULL JOIN courses AS c
ON s.course_id = c.course_id;

Result:

• Rows without matches are filled with NULL values.

Example 2: Filtering Unmatched Rows

SELECT s.name, c.course_name
FROM students AS s
FULL JOIN courses AS c
ON s.course_id = c.course_id
WHERE s.course_id IS NULL OR c.course_id IS NULL;

Result:

• This query finds rows that have no matching records in the other table.

Benefits of FULL JOIN

1. Complete Data View: Includes all rows from both tables.
2. Identify Gaps: Highlights unmatched rows for debugging and analysis.
3. Versatile Data Combination: Works for complex datasets and scenarios.

Real-World Applications

1. Education Systems: Match students with courses and identify students or courses without associations.
2. Inventory Management: Combine supplier and product data, identifying missing links.
3. Financial Reporting: Highlight unmatched transactions or accounts.

Common Use Cases

1. Data Validation: Ensure data consistency and integrity across tables.
2. Reporting: Generate comprehensive views of related datasets.
3. Data Integration: Combine data from multiple sources into a unified format.

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Conclusion

PostgreSQL FULL JOIN is a powerful SQL operation that enables you to combine and analyze datasets comprehensively. By mastering this feature, you’ll enhance your ability to handle relational databases effectively.

Stay tuned to The Coding College for more database tutorials and expert guidance!