mvc

exercises/2-optimizing-queries/README.md

@@ -0,0 +1,58 @@
+## Optimizing Queries and Data Comparisons
+
+This challenge will take what we already know about SQL and Python and add the necessary tools to optimize how we make queries and compare data.
+
+#### Setup
+
+In create_db.py, initialize and create a new database "schedules.db" and give it the necessary tables to hold the following:
+
+Students have a name, and a major.
+Classes have a title, and a field of study.
+
+Major and field of study are the same, ie. Economics is a major and a field of study.
+
+Students have many classes.
+Classes have many students.
+
+Write a seed_db() function that takes the existing data in create db and randomly fills the database with it.
+
+
+#### Query
+
+Write a function shared_classes() in Python that takes two student names. It should return the classes they take together, if any. How you want to do this is open ended.
+
+What is the Big O time complexity of your algorithm for loading the students and comparing their classes? Write it down, and benchmark your code.
+
+#### First Optimization - the Index
+
+Read [how indexes work](http://www.programmerinterview.com/index.php/database-sql/what-is-an-index/) here. What type of data structure does sqlite3 use to hold indexes?
+
+Now, add an index to one or more of your tables on columns you think would be appropriate.
+
+Benchmark again - what is your speed now?
+
+#### Second Optimization - use a Set
+
+Are you comparing the data returned from the DB in Python? If so, you probably aren't using the right data type. We haven't covered Sets yet - read about them [here](https://docs.python.org/3.4/library/stdtypes.html#set)
+
+A set is very similar to a dictionary, only it does not store values. Only keys. The syntax is like so:
+```
+{'Programming', 'Calculus', 'Literature'}
+```
+Use sets to store the returned class data about both students and use set's built in methods to find the intersection if it exists.
+
+The Big O complexity of this operation is `O(len(x) * len(y))`. If you did the most simple comparison with arrays, it was probably `O(len(x) * len(y)**2)`.
+
+Read about sets. Why is this? Here's a [list](https://wiki.python.org/moin/TimeComplexity) of all Python datatype method's time complexity.
+
+#### Third Optimization - a better (longer!) Query
+
+Instead of doing all your comparisons on the Python side, can we pull the information straight out of the database with a more advanced query?
+
+Before you write the query to replace your original answers- let's write a new function that takes a Major and number of students, and returns classes where that number of students or more in that class have that major.
+
+Now, write your enhanced query to find the intersect without any Python data parsing.
+
+Benchmark this function against your first two.
+
+Sandbox!! You will want to get familiar with the following SQL commands: GROUP BY, HAVING, IN.