19.10 Equi Joins

  • A left join is often called an equi join because it describes the relationship between the two tables where the keys are equal.

  • inner_join(), right_join(), full_join() are similar to left_join() in that respect, but the difference is which rows they keep:

    • left join keeps all the rows in x,

    • the right join keeps all rows in y,

    • the full join keeps all rows in either x or y, and

    • the inner join only keeps rows that occur in both x and y

  • Equi joins are the most common type of join, so we’ll typically omit the equi prefix, and just say “inner join” rather than “equi inner join”.

Outer joins

Figure 19.3: Outer joins

inner join

Figure 19.4: inner join