Code&Data Insights

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..

[ Discrete random variables : Bernoulli / Binomial / Geometric / Poisson ]

Marcov's Inequality : For a continuous nonnegative random variable X, and c>0, then * One of the application of E(x)* Chebyshev's Theorem : a fact that applies to all possible data sets. It describes the minimum proportion of the measurements that lie must within one, two, or more standard deviations of the mean. Conditional Probability P(A | B) = P(A and B) / P(B) : a measure of an event occuri..