The dataset on the left-hand side of a join will be present in the output dataset irrespective of the matching records that the connecting dataset has. The following diagram is an illustration of a left join Venn diagram:
In the previous hospital inner join example, we had a list where recipients and donors matched. The hospital might be interested in retaining its recipient list and flagging instances when the donor is available. In such an instance a left joint becomes important.
In the case of the Class table, if we want to retain all the information and add on the information of the Interests table, we can use a left joint where ...
