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Has Many Relationships

To run sql statements from an external file, load them into your RDBMS client and run the commands from there.

SQL 1-n Relationships and Joins Exercise in PostgreSQL

Setup schema and relationships

  1. Create a new postgres user named has_many_user
  2. Create a new database named has_many_blogs owned by has_many_user
  3. Before each create table statement, add a drop table if exists statement.
  4. In has_many_blogs.sql Create the tables (including any PKs, Indexes, and Constraints that you may need) to fulfill the requirements of the has_many_blogs schema below.
  5. Create the necessary FKs needed to relate the tables according to the relationship table below.
  6. Run the provided scripts/blog_data.sql

has_many_blogs schema

users

Column Name Datatype NULL Default
id (PK) serial false auto incrementing
username character varying (90) false
first_name character varying (90) true NULL
last_name character varying (90) true NULL
created_at timestamp (with tz) false now()
updated_at timestamp (with tz) false now()

posts

Column Name Datatype NULL Default
id (PK) serial false auto incrementing
title character varying (180) true NULL
url character varying (510) true NULL
content text true NULL
created_at timestamp (with tz) false now()
updated_at timestamp (with tz) false now()

comments

Column Name Datatype NULL Default
id (PK) serial false auto incrementing
body character varying (510) true NULL
created_at timestamp (with tz) false now()
updated_at timestamp (with tz) false now()

Relationship Table

Table Name Relationship Table Name
users Has Many posts
users Has Many comments
posts Has Many comments
posts Belongs To users
comments Belongs To users
comments Belongs To posts

Reading relationship information in a table format can be difficult, whiteboarding the relationship model in UML/ERD format is highly recommended required.

Queries across multiple tables

Write the following SQL statements in joins.sql

  1. Create a query to get all fields from the users table
  2. Create a query to get all fields from the posts table where the user_id is 100
  3. Create a query to get all posts fields, the user's first name, and the user's last name, from the posts table where the user's id is 200
  4. Create a query to get all posts fields, and the user's username, from the posts table where the user's first name is 'Norene' and the user's last_name is 'Schmitt'
  5. Create a query to get usernames from the users table where the user has created a post after January 1, 2015
  6. Create a query to get the post title, post content, and user's username where the user who created the post joined before January 1, 2015
  7. Create a query to get the all rows in the comments table, showing post title (aliased as 'Post Title'), and the all the comment's fields
  8. Create a query to get the all rows in the comments table, showing post title (aliased as post_title), post url (ailased as post_url), and the comment body (aliased as comment_body) where the post was created before January 1, 2015
  9. Create a query to get the all rows in the comments table, showing post title (aliased as post_title), post url (ailased as post_url), and the comment body (aliased as comment_body) where the post was created after January 1, 2015
  10. Create a query to get the all rows in the comments table, showing post title (aliased as post_title), post url (ailased as post_url), and the comment body (aliased as comment_body) where the comment body contains the word 'USB'
  11. Create a query to get the post title (aliased as post_title), first name of the author of the post, last name of the author of the post, and comment body (aliased to comment_body), where the comment body contains the word 'matrix' ( should have 855 results )
  12. Create a query to get the first name of the author of the comment, last name of the author of the comment, and comment body (aliased to comment_body), where the comment body contains the word 'SSL' and the post content contains the word 'dolorum' ( should have 102 results )
  13. Create a query to get the first name of the author of the post (aliased to post_author_first_name), last name of the author of the post (aliased to post_author_last_name), the post title (aliased to post_title), username of the author of the comment (aliased to comment_author_username), and comment body (aliased to comment_body), where the comment body contains the word 'SSL' or 'firewall' and the post content contains the word 'nemo' ( should have 218 results )

Additional Queries

If you finish early, perform and record the following SQL statements in joins.sql using these higher level requirements.

  1. Count how many comments have been written on posts that have been created after July 14, 2015 ( should have one result, the value of the count should be 27)
  2. Find all users who comment about 'programming' ( should have 337 results)