Simple Query

[gamm...@gmail.com]

Dear Robbie,

assume we have an employee collection and each employee has a salary. How would you perform

the following query using yap database: "Which employee has the highest salary?"

Thank you!

[Robbie Hanson]

Start by creating a secondary index:

https://github.com/yapstudios/YapDatabase/wiki/Secondary-Indexes

You’ll want to include employee.salary in your index. (Of course, you’re not limited to just one item in a secondary index, so you can include other things as well.)

Once that’s up, you’re ready to execute queries against the secondary index.

> "Which employee has the highest salary?"

Technically, you might have multiple employees that all have the same salary, which is also the highest salary in the company. So I’d actually break it up into 2 queries:

1. What’s the MAX(salary) ?

2. Enumerate the employees WHERE salary = max_salary

So query #1 is an aggregate query:

https://github.com/yapstudios/YapDatabase/wiki/Secondary-Indexes#aggregate-queries

And query #2 is a standard query (now that you know max_salary):

https://github.com/yapstudios/YapDatabase/wiki/Secondary-Indexes#standard-queries

Hope that helps.

-Robbie Hanson

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