Code&Data Insights

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..

Key difference between SQL Keys SQL keys are used to uniquely identify rows in a table. SQL keys can either be a single column or a group of columns. Super key is a single key or a group of multiple keys that can uniquely identify tuples in a table. Super keys can contain redundant attributes that might not be important for identifying tuples. Candidate keys are a subset of Super keys. They cont..

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 ..

Covariance : ​Covariance and Correlation, both describe the relationship between two numerical variables. How to get a covariance value between X and Y? 1) Find the deviation from X to x. (Y and y) ------------> (x- x) and (y- y) 2) multiply (x- x) and (y- y) 3) Add the values, find the sum 4) divide by n-1 -> WHY did we divide by n-1, not just n? : " Degrees of Freedom" - We can't calculate the..

[ Probability Theory ] Probability theory is the study of uncertainty. It is about the concepts from probability theory for deriving machine learning algorithms and delves(=examines) into a branch of analysis known as measure theory. 1 Elements of probability - Sample Space Ω : The set of all the outcomes of a random experiment. - Sets of Events(=event space) : F: A set whose elements A ∈ F(call..