Joins in Tableau: Inner, outer, left, or a right join in Tableau

Key Takeaways

one of the most important aspects of your work in tableau is the data source you are using to perform analysis quite often the data will be stored in multiple locations and hence you will have to deal with a number of data sources which live in different environments nevertheless you are going to want to use all of the data available to you and run analysis on everything together the way we merge multiple data sources is by using joins for those of you who have already followed our program and especially our SQL videos you'll be familiar with what follows in this video so feel free to skip or continue watching as a refresher for the rest please follow along when we want to perform cross data table joins we want to combine two or more data tables to create a unique database how do we join separate data tables well there are a few ways to do that we can create an inner outer left or a right join let's open an excel file to demonstrate a bit better what each type of join represents here we have two very simple tables the first one shows us the age of three basketball players and the second one shows us the salary of basketball players please note that the two tables are different due to their last rows we have LeBron James in the first one and Kyrie Irving in the second okay let's say we would like to run some analysis and use the data available in both tables therefore as described earlier we have to use joints but how do we do that we can easily see that the two tables have one column in common the basketball player column this column will serve as a key when we put together the information from both tables a left join would mean that the left column of the first table will lead the way we will use it to create a table containing age and salary information about the three players we see here whenever we find one of these players to the right we'll add their salary in the new table as you can see here if their name is not present to the right which is the case with LeBron James's salary we will have a null value in the table if a player's name is not present in the left column of the first table we will not include any information about them as this is a left join and any rows which are not present in the key field of the left table are omitted in the new table a right join functions in the same way however this time the left column of the second table leads the way Kyrie Irving replaces LeBron James who is not present in the left table hence the only missing value would be Kyrie Irving's H given that the only information we have about him is in the right table the case when we are interested in the intersection of the two tables only is called an inner join this is when we create a table that contains rows where we have an exact match between the key fields we are joining the two tables with in our case basketball player this time the newly created table contains two rows only both tables contain information about these players hence this is an inner join an outer join would be the opposite case we add all rows of the two tables regardless of whether there is a match in the key field we are linking with when there isn't we would have null values which is the case with both LeBron James and Kyrie Irving here these are the main principles you need to understand when deciding whether to create a left right inner or outer join in tableau depending on your needs and the specific case you were working on you will be able to apply one of these structures and join your data