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 è Mysql, mongoDB, … è Provide convenient, efficient, and secure access and manipulation of large amounts of data è Controls access to shared data from multiple, simultaneous users with properties Atomicity, Consisten..

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 ..