apache derby where clause

In Apache Derby, the WHERE clause is used in SELECT, UPDATE, and DELETE statements to filter the rows returned or affected by the query based on a specific condition. Here is the basic syntax of a WHERE clause:

SELECT column1, column2, ...
FROM table_name
WHERE condition;

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

DELETE FROM table_name
WHERE condition;

In each of these statements, the WHERE clause is used to specify which rows should be selected, updated, or deleted based on the condition that is specified. The condition can be a comparison between columns or values, a logical expression combining multiple conditions, or a subquery returning a set of values to compare against.

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

SELECT name, age, email
FROM students
WHERE age > 30;

This statement selects the name, age, and email columns from the students table where the age column is greater than 30.

UPDATE students
SET age = 26
WHERE name = 'John Doe';

This statement updates the age column in the students table to a new value of 26 for the row where the name column is equal to 'John Doe'.

DELETE FROM students
WHERE age < 18;

This statement deletes all rows from the students table where the age column is less than 18.

By using the WHERE clause in Apache Derby, you can create powerful queries that filter and manipulate your data based on specific conditions. It's important to be careful when using the WHERE 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.