apache derby group by clause

In Apache Derby, the GROUP BY clause is used in conjunction with the SELECT statement to group rows of data that have the same values in one or more columns. The GROUP BY clause can be used to calculate aggregate functions like COUNT, SUM, AVG, MAX, and MIN for each group of rows.

Here is the basic syntax of a GROUP BY clause:

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

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. You can group by one or more columns, and you can apply one or more aggregate functions to each group.

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

SELECT gender, COUNT(*)
FROM students
GROUP BY gender;

This statement groups the rows in the students table by the gender column and returns the count of rows in each group.

SELECT year, AVG(gpa), MAX(gpa), MIN(gpa)
FROM students
GROUP BY year;

This statement groups the rows in the students table by the year column and returns the average, maximum, and minimum gpa for each group.

SELECT gender, year, AVG(age)
FROM students
GROUP BY gender, year;

This statement groups the rows in the students table by both the gender and year columns and returns the average age for each combination of gender and year.

By using the GROUP BY clause in Apache Derby, you can create powerful queries that group and aggregate your data based on specific criteria. It's important to be careful when using the GROUP BY 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.