Combine datasets using Pandas merge(), join(), concat() and append()

In the world of Data Bases, Joins and Unions are the most critical and frequently performed operations. Almost every other query is an amalgamation of either a join or a union. Using Pandas we perform similar kinds of stuff while working on a Data Science algorithm or any ETL (Extract Transform and Load) project, joins and unions are critical here as well. Just a little difference between join and unions before jumping onto the use cases of both. Both join and union are used to combine data sets, however, the result set of a join is a horizontal combination of the dataset where a result set of a union is a vertical combination of data set.