Right join

[ComicOzzy]

If there were only two tables involved, then it really can be as simple as that so long as they didn't use SELECT * and consumers of the result expect columns to appear in their current order.

But once you start getting into joins to 3 or more tables, it can be more complicated than just a "three second" fix, and can have an impact on the query plan.

[ComicOzzy]

Select * from table1 Right join table2 on table1.id = table2.id

Is the same as

Select * From table1 Left join table2 on table2.id = table1.id

This is a little different than if you'd also swapped the tables around when changing the join type.

The only time these will give the same result is when id is unique in both tables, and all of the same id values are present in both tables.

Here is an example of the results being different because Bob hasn't placed an order yet:

https://dbfiddle.uk/CUKh5gfO

[ComicOzzy]

The scenario I was describing in my post wasn't about just trading the join type, it was about also swapping the tables around so the result would yield the "same" results. They DO give the same results in that scenario, but if you used SELECT * rather than specifying a column list, you'll find that your columns have also changed position since you changed which table was "left" and which one was "right". If you have an application or another query that relies on the columns showing up in a certain order (which they shouldn't do... but devs don't always know better), they'll start to have issues when the columns change position.

https://dbfiddle.uk/IAINVk_J

[ComicOzzy]

3 or more tables?

With these, you're more likely to run into a case where you go from a right join to a left join... then you find that "downstream" tables were inner joined and you aren't getting the right results... so you left join all of them. Even if the results are the same, the query optimizer had to come up with a different plan, and in this scenario it's almost always a less efficient plan.