A "derived field" in refers to a field (or column) whose value is calculated or derived from one or more other fields in the database.
This can be achieved through a database query, often using SQL
In SQL, a derived field is a field that is based on other fields in the table.
Derived Field Example
Suppose you have a database table named sales with two columns: quantity and unit_price.
You want to create a derived field total_price, which is the product of quantity and unit_price.
The SQL query to achieve this would be:
SELECT quantity, unit_price, (quantity * unit_price) AS total_price FROM sales;
Derived fields can be renamed using the SQL keyword in the SELECT statement.
Parameter Query
A parameter query in a database is a type of query where one or more of the criteria for the query are provided as parameters, rather than being hard-coded in the query itself.
This approach is commonly used to create flexible and dynamic queries, allowing users to specify the exact criteria for the query at runtime.
When using a parameter query, the user is prompted to enter a for the parameter.
Parameter Query Example
The SQL query might look something like this:
SELECT id, name FROM employees WHERE department = ?;
In this query, the ? is a placeholder for the department parameter. When you run this query, you'll provide the actual department name as a parameter.
When constructing SQL queries dynamically, it's important to always sanitize and validate to prevent SQL injection attacks. Use parameterized queries or prepared statements to bind the user input to the query.
Boolean Operators
In SQL, Boolean operators are used to form conditions in queries, allowing you to filter data based on specific criteria. The primary Boolean operators in SQL are AND, OR, and NOT.
Boolean Operators Example
SELECT * FROM employees WHERE (department = 'Sales' OR department = 'Marketing') AND salary > 50000;
In this query, the parentheses ensure that the OR condition is evaluated first, and then the AND condition.
