Combining Oracle SQL Queries with the UNION Clause

When working with Oracle SQL, you may find yourself needing to combine the results of several queries into a single output. This can be useful when you want to obtain a summary or consolidate data from different tables into a complete view. In this article, I will show you how to achieve this using the UNION clause in Oracle SQL. Join me as we explore this powerful feature.

The UNION Clause

The UNION clause is used to combine the results of two or more queries into a single result table. It is important to note that the UNION clause can only be used to combine result sets with the same column structure. This means that the columns in the queries must have the same names and data types.

Use Cases

Suppose you have a table called “empleados” in your Oracle database and want to obtain a count of employees by department as well as a total count of all employees. We can achieve this with the UNION clause. Let us look at an example:

SELECT departamento, COUNT(*) as total_por_departamento
FROM empleados
GROUP BY departamento

UNION ALL

SELECT 'Total' as departamento, COUNT(*) as total_general
FROM empleados;

In this example, we select the “departamento” column and use the COUNT aggregate function to count the number of records in each department. The first query counts by department, while the second query calculates the grand total. The UNION ALL clause combines the results of both queries into a single output.

When executing this query, we will obtain a result table containing two columns: “departamento” and “total_por_departamento”. The last row will have the value “Total” in the “departamento” column and display the grand total in the “total_por_departamento” column.

To Wrap Up…

The UNION clause in Oracle SQL is a powerful tool for combining query results into a single output. You can use it to consolidate data from different tables or summarize information in a complete view. In this article, we saw how to combine queries that count by department and calculate a grand total. Remember that the queries used with the UNION clause must have the same column structure.

I hope this article has been useful! You now have another tool in your Oracle SQL toolkit for combining queries and obtaining accurate, complete results. Explore the UNION clause further and experiment with different queries to optimize your data analysis.