apache derby having clause

In Apache Derby, the HAVING clause is used in conjunction with the GROUP BY clause to filter the results of an aggregate query based on a specific condition. The HAVING clause is similar to the WHERE clause, but it operates on groups of rows rather than individual rows.

Here is the basic syntax of a HAVING clause:

SELECT column1, column2, ..., aggregate_function(column_name)
FROM table_name
GROUP BY column1, column2, ...
HAVING condition;

In this syntax, the column1, column2, etc. are the columns that you want to group by, and the aggregate_function(column_name) is the function that you want to apply to each group. The condition in the HAVING clause specifies the condition that must be met by each group in order to be included in the result set.

Here are some examples of using the HAVING clause in Apache Derby:

SELECT gender, AVG(gpa)
FROM students
GROUP BY gender
HAVING AVG(gpa) > 3.0;

This statement groups the rows in the students table by the gender column and returns the average gpa for each group. The HAVING clause filters the groups and only returns those with an average gpa greater than 3.0.

SELECT year, COUNT(*)
FROM students
GROUP BY year
HAVING COUNT(*) > 10;

This statement groups the rows in the students table by the year column and returns the count of rows in each group. The HAVING clause filters the groups and only returns those with a count greater than 10.

By using the HAVING clause in Apache Derby, you can create powerful queries that filter your data based on specific criteria after grouping it by one or more columns. It's important to be careful when using the HAVING clause, as it can have a significant impact on your data integrity and application behavior. Always make sure to test your queries on a copy of your data before running them on your live database.