Code&Data Insights

Schemas and Instances - Databases instance: the current content of the DB - Databases schema: the structure of the data(relations/classes) -> Relation(table) is as a set or tuple! What is the meaning of Data Independence?? : the ability to modify definition of schema at one level with little or no effect on the schema at a high level - Logical data independence: adding new fields to a record or ..

What is a Database?: a collection (Not a random pile of data) of data that exists over a long period time. DBMS: a complex software package developed to store and manage databases- Mysql, mongoDB, …- Provide convenient, efficient, and secure access and manipulation of large amounts of data- Controls access to shared data from multiple, simultaneous users with properties Atomicity, Consistency, l..

5. Give details of employees who worked in at least two different facilities. Details include employee’s first-name, last-name, start date, end date, facility name, role (nurse, doctor, etc.), Medicare card number, telephone-number, and email address. Results should be displayed sorted in ascending order by first name, then by last name, then by start date. QUERY)  SELECT e.firstName, e.lastName..

Inner Join : selects records that have matching values in both tables. => intersection of two tables SELECT column_name(s) FROM table1 INNER JOIN table2 ON table1.column_name = table2.column_name; Left Join SELECT column_name(s) FROM table1 LEFT JOIN table2 ON table1.column_name = table2.column_name; Right Join SELECT column_name(s) FROM table1 RIGHT JOIN table2 ..

What is a NULL Value? : NULL value is a filed with no value. NULL is not value, it's just a place holder ** Therefore, we can't compare between NULL values! Null is unknown, so they can't be same ! null != null Can we test for NULL? : Yes, it's possible to test for using IS NULL & IS NOT NULL NULL Value with Groung and Aggregating : Nulls are counted when grouping, but ig..

Databases : an organized collection of data that exists over a long period of time ( Persistent storage ) - collection of data about different kinds of individuals(Entities) and the relationship between individuals. DBMS ( Database Management System ) : a complex software package developed to store and mange databases - supports convenient, efficient, and secure access and manipulation of large ..