From the course: Advanced SQL for Data Scientists
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Bitmap indexes
- [Instructor] Let's take a look at bitmap indexes. Now, a bitmap index is relatively simple. It's quite different from a B-tree index and the basic idea is when we have a column that has a small number of possible values, we might be able to map those values or encode them in a bit string. So for example, here we have a table and there's an ID column and another column which is_union_member and you can see we list yes or no or null. And we could use literally those strings. Alternatively, we could map a yes to a one, a no to a zero and a null to a zero zero. And that's what we've done in the two columns on the right. Now, it doesn't have to be just two values. You can have a larger number of possible values. For example, in this new table here on the right where we have an ID and pay_type, we have three different kinds of pay type: salary, hourly, and contractor. Now, you'll notice the salary column has a one in it…
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