shady-mungai / phase-3-sql-organizing-bears-lab

Organizing Bears Lab

Learning Goals

• Use the CREATE TABLE command to create a new table with various data types
• Use the INSERT INTO command to insert data (i.e. rows) into a database table
• Use the SELECT command with various functions and modifiers to write queries

Lab Structure

This lab might seem a bit different than what you've seen before. Take a look at the file structure and read the comments to understand what each file is used for:

├── Gemfile
├── README.md
├── config
│   └── environment.rb # requires bundler and files
├── lib
│   ├── create.sql     # where you CREATE your schema
│   ├── insert.sql     # where you INSERT your data
│   ├── seed.sql       # data for in-memory test database
│   ├── sql_queries.rb # where you write your SELECT queries
└── spec               # all the specs
    ├── create_spec.rb # this tests your create.sql file
    ├── insert_spec.rb # this tests your insert.sql file
    ├── select_spec.rb # this tests the queries you write in sql_queries.rb
    └── spec_helper.rb

This lab uses the sqlite3 gem to allow us to connect to a SQL database from Ruby. How cool is that!? We'll use this gem more in the lessons to come.

To install the sqlite3 gem, run:

$ bundle install

Running bundle install is a good habit to get into when setting up new Ruby applications with a Gemfile. As a reminder, the Gemfile is where we specify the dependencies for a Ruby application. Running bundle install will download the gems listed in this file to your system.

In case you forget though, running learn test will also run bundle install if you haven't already installed the necessary gems.

A Note on Testing

Let's briefly go over what is happening in setup blocks that our tests will be using.

let(:db) do
  SQLite3::Database.new(':memory:')
end

before do
  sql = File.read("lib/create.sql")
  db.execute_batch(sql)
end

Before each test, two important things happen.

First, a new in-memory database is created. Why do we do this instead of creating a database file? Let's say we run our tests and they add ten items to our database. If we did not use an in-memory store, those would be in there forever. This way, our database gets thrown out after every running of the tests. You can learn more about in-memory databases here.

Next, the test opens the .sql file, and runs the SQL code in that file in that in-memory database.

Part 1: CREATE TABLE

Get the tests in spec/create_spec.rb to pass by writing code in the lib/create.sql file. Your CREATE statement should look something like this:

CREATE TABLE bears (
  //columns here
);

Your columns should be the following types:

column	type
id	integer
name	text
age	integer
sex	text
color	text
temperament	text
alive	boolean

Read about SQLite3 Datatypes to determine what your insert values are going to be. Be sure to pay attention to how booleans are expressed in SQLite3.

Part 2: INSERT

Get the tests in spec/insert_spec.rb to pass by writing code in the lib/insert.sql file. Input the following 8 bears (you can make up details about them, but make sex either 'M' or 'F'):

• Mr. Chocolate
• Rowdy
• Tabitha
• Sergeant Brown
• Melissa
• Grinch
• Wendy
• unnamed (refer back to how to create a record that doesn't have one value)

Part 3: SELECT

Get the tests in spec/select_spec.rb to pass. Note that for this section, the database will be seeded with external data from the lib/seed.sql file so don't expect it to reflect the data you added above.

Note: Since it's a Ruby file, write your queries as strings within methods in the lib/sql_queries.rb file. For example, to pass the first test, your Ruby method should look like this:

def selects_all_female_bears_return_name_and_age
  "SELECT bears.name, bears.age FROM bears WHERE sex='F';"
end

You can also write the SQL strings in a Ruby heredoc to help with formatting:

def selects_all_female_bears_return_name_and_age
  <<-SQL
    SELECT
      bears.name,
      bears.age
    FROM
      bears
    WHERE
      sex='F';
  SQL
end

You may be expected to use SQL statements that you're not particularly familiar with. Make sure you use the resources and Google to find the right statements.

Resources

• SQL Datatypes
• SQL GROUP BY