afelix997 / -sql-schema-modifications

Schema Modifications

Database schemas reflect the current approach to solving a problem. Over time, the problem or the solution are bound to change.

While it's preferable to modify application code instead of schema changes, a schema that doesn't fit the current understanding of the problem can cause all sorts of problems downstream:

• duplication of data
• incorrect stored values (e.g. if the column type is incorrect)
• complicated or non-intutive code
• interfaces that don't match how a user perceives the problem
• limitations that prevent users from fully harnessing the application

In this challenge you don't have to consider any existing application code, but schema changes often require careful coordination with application code. Your task is to update an existing schema that has a few bugs and limitations. You'll be renaming columns, changing column types and adding missing constraints.

Current Schema

You're working with the city's water department database. There are two tables, customers and statements. Statements are effectively the bill a customer receives each month.

customers

column	type
id	integer, auto increment
first	text
last	text
social	varchar(255)
account_number	varchar(255)
line_1	varchar(255)
city	varchar(255)
state	varchar(255)
zip	varchar(255)
current_balance_cents	integer

bills

column	type
id	integer, auto increment
customer_id	integer
gallons_used	integer
cents_per_gallon	integer
start_date	date
end_date	date
status	varchar(255)
payment_date	date
due_date	date
amount_due_cents	integer
min_amount_due_cents	integer

Check everything!

Make sure that when you enter your database that you see everything you want to see.

Modifications

Save your schema migration to a new file, migrations.sql. Write SQL statements to make the following modifications:

Use the following link to assist you in writing queries for your migration file -> ALTER TABLE statement

customers

1. Both columns first and last have ambiguous names. Rename them to first_name and last_name.
2. Because the current column type of first and last are text, these columns have almost no limit to how much content they can store. We've noticed garbage registrations with first and last names over 20kb! Change the column types of these to a varchar with a max of 255 characters.
3. The social column also has some dirty data, some customers have entered their social with dashes, others without, others with spaces. We've decided to store only the numbers of a users social. Which means all social values should be exactly 9 characters. Change the column type to allow only 9 characters.
4. The account_number column has the same issue, the city's account numbers are 14 characters. Update the column type.
5. Someone forgot to add a line_2 column, add one.
6. The zip column is currently an integer, but we're loosing digits from customers with zip codes that start with zeros. Change the column type appropriately.
7. Remove the current_balance_cents column. It was added for performance reasons, but there's a bug in the application code and it's often out of date.

statements

1. The customer_id column allows null values, change it so a value is required.
2. We've updated our water meters and we can accurately measure fractional gallons. Update gallons_used to allow for two decimal places.
3. Add a default value "payment_due" to status.

Final Steps

Add your migration file into your database. Does it change your schema? Are the columns and tables updated? What do you notice about the relationship between migrations and the original SQL file?