How to Use Oracle Group By in 2024?

In Oracle, the GROUP BY clause is used in conjunction with the SELECT statement to group rows that have the same values in specified columns. This allows for the aggregation of data based on those columns.

When using the GROUP BY clause, you must specify the columns by which you want to group the data. Additionally, you can also include aggregate functions such as COUNT, SUM, AVG, MIN, MAX, etc., to perform calculations on the grouped data.

It's important to note that when using the GROUP BY clause, any column in the SELECT statement that is not part of an aggregate function must be included in the GROUP BY clause. Otherwise, an error will be thrown.

Here is an example of how to use the GROUP BY clause in Oracle:

SELECT department_id, COUNT(employee_id) FROM employees GROUP BY department_id;

In this example, we are grouping the employees table by the department_id column and counting the number of employee_ids in each department.

How to use Oracle GROUP BY to create subtotals or summary reports?

To use Oracle GROUP BY to create subtotals or summary reports, follow these steps:

Write a SELECT statement that includes the columns you want to summarize and group by. For example:

1
2
3

SELECT column1, SUM(column2)
FROM table
GROUP BY column1;

Use the GROUP BY clause to group the results based on a specific column or expression.
Use aggregate functions like SUM, COUNT, AVG, etc. in the SELECT statement to perform the summary calculations.
Run the query to generate the summary report with subtotals for each group defined in the GROUP BY clause.

For example, let's say you have a table named 'sales' with columns 'product', 'region', and 'revenue'. To create a summary report that shows total revenue for each region, you can use the following query:

1
2
3

SELECT region, SUM(revenue) as total_revenue
FROM sales
GROUP BY region;

This will group the sales data by region and calculate the total revenue for each region. The result will be a summary report with subtotals for each region.

How to use Oracle GROUP BY with the CONNECT BY clause for hierarchical queries?

To use Oracle GROUP BY with the CONNECT BY clause for hierarchical queries, you can follow these steps:

Write a query that uses the CONNECT BY clause to define the hierarchical relationship between rows in your dataset. For example:

SELECT employee_id, employee_name, manager_id
FROM employees
START WITH manager_id IS NULL
CONNECT BY PRIOR employee_id = manager_id;

Use the GROUP BY clause to aggregate the data based on a specific column or columns. For example, if you want to find the number of employees reporting to each manager, you can use the following query:

SELECT manager_id, COUNT(employee_id) as num_employees
FROM employees
START WITH manager_id IS NULL
CONNECT BY PRIOR employee_id = manager_id
GROUP BY manager_id;

You can also use other aggregate functions in combination with the GROUP BY clause, such as SUM, AVG, MIN, and MAX, to perform calculations on the grouped data. For example, to find the total salary amount for employees reporting to each manager, you can use the following query:

SELECT manager_id, SUM(salary) as total_salary
FROM employees
START WITH manager_id IS NULL
CONNECT BY PRIOR employee_id = manager_id
GROUP BY manager_id;

By combining the CONNECT BY clause with the GROUP BY clause in Oracle, you can perform hierarchical queries and aggregate the data based on specific criteria.

How to use Oracle GROUP BY with the GROUPING SETS operation for more advanced grouping?

To use Oracle GROUP BY with the GROUPING SETS operation for more advanced grouping, you can follow these steps:

Write a SQL query that includes the GROUP BY clause and specifies the columns you want to group by.
Use the GROUPING SETS operator in the GROUP BY clause to specify the different groupings you want to perform. You can include multiple columns or expressions in the GROUPING SETS clause to create different combinations of groupings.
Execute the query to retrieve the results with the grouped data according to the specified groupings.

For example, consider the following SQL query that uses GROUPING SETS to perform advanced grouping:

1
2
3

SELECT department_id, job_id, COUNT(*) as employee_count
FROM employees
GROUP BY GROUPING SETS ((department_id), (job_id), (department_id, job_id));

In this query, we are grouping the employees by department_id, job_id, and both department_id and job_id. The results will include the total employee count for each combination of groupings specified in the GROUPING SETS clause.

By using the GROUPING SETS operation in combination with the GROUP BY clause, you can perform more advanced and flexible grouping operations in Oracle SQL.

How to use Oracle GROUP BY with the WITH clause for recursive queries?

To use Oracle GROUP BY with the WITH clause for recursive queries, you can follow these steps:

Define the recursive query using the WITH clause.
Use the GROUP BY clause in the main query to group the results based on a specific column or expression.
Include any required aggregate functions in the SELECT statement to perform calculations on the grouped data.
Order the results using the ORDER BY clause if needed.

Here is an example of using Oracle GROUP BY with the WITH clause for a recursive query:

WITH RECURSIVE cte AS (
  SELECT
    employee_id,
    manager_id,
    level
  FROM
    employees
  WHERE
    manager_id IS NULL
  UNION ALL
  SELECT
    e.employee_id,
    e.manager_id,
    c.level + 1
  FROM
    employees e
  JOIN
    cte c ON c.employee_id = e.manager_id
)

SELECT
  manager_id,
  COUNT(employee_id) as num_employees,
  MAX(level) as max_depth
FROM
  cte
GROUP BY
  manager_id
ORDER BY
  manager_id;

In this example, we are using a recursive CTE (Common Table Expression) to calculate the number of employees reporting to each manager and the maximum level of hierarchy depth. The results are then grouped by the manager_id column using the GROUP BY clause, and aggregate functions like COUNT and MAX are used in the SELECT statement to perform calculations on the grouped data. Finally, the results are ordered by the manager_id column using the ORDER BY clause.

How to use Oracle GROUP BY with the HAVING clause to filter grouped rows?

To use Oracle GROUP BY with the HAVING clause to filter grouped rows, you can follow these steps:

Start by writing a SQL query that includes the GROUP BY clause to group rows based on a specific column or set of columns.
After the GROUP BY clause, add the HAVING clause to apply a filter condition to the grouped rows. The HAVING clause is similar to the WHERE clause but is used specifically with aggregated data.
In the HAVING clause, specify the filter condition that you want to apply to the grouped rows. This condition can include aggregate functions such as COUNT, SUM, AVG, MIN, or MAX.
Run the SQL query to see the results of the grouped rows that meet the specified filter condition.

For example, let's say you have a table called "sales" with columns "product_id" and "quantity_sold." You want to group the rows by product_id and only show products that have a total quantity_sold greater than 100. Here is how you can write the SQL query:

SELECT product_id, SUM(quantity_sold) as total_quantity_sold
FROM sales
GROUP BY product_id
HAVING SUM(quantity_sold) > 100;

This query will group rows by product_id and calculate the total quantity_sold for each product. It will then filter out products that have a total quantity_sold less than or equal to 100 using the HAVING clause.

How to use Oracle GROUP BY to generate pivot tables or cross-tabulations?

To use Oracle GROUP BY to generate pivot tables or cross-tabulations, you can use the PIVOT clause in combination with the GROUP BY statement. Here is an example query:

SELECT * FROM ( SELECT column1, column2, column3 FROM your_table ) PIVOT ( COUNT(column3) FOR column2 IN ('value1' as value1, 'value2' as value2, 'value3' as value3) ) ORDER BY column1;

In this query:

Replace "your_table" with the name of your table.
Replace "column1", "column2", and "column3" with the actual column names you want to display in your pivot table.
Replace 'value1', 'value2', and 'value3' with the actual values you want to pivot on.

This query will generate a pivot table with column1 as rows, column2 values as columns, and the count of column3 as the values in the table.

You can customize the query further by using aggregate functions like SUM, AVG, MAX, MIN, etc., in place of COUNT to calculate different values in the pivot table.

techtalk.abatek.com

How to Use Oracle Group By?