SQL Practice

Getting Started

• Fork and Clone

Creating Our Database

$ createdb library

Note that this is a command-line utility that ships with Postgres, as an alternate to using the SQL command CREATE DATABASE library; inside psql.

That means you should run this command from your Zsh prompt -- not from inside psql.

Inspecting The Schema

Look critically at each line of the provided schema.sql file. Here's how one row breaks down...

id SERIAL PRIMARY KEY

• id: column name, how we will refer to this column
• SERIAL: the data type (similar to integer or string). It's a special datatype for unique identifier columns, which the db auto-increments.
• PRIMARY KEY: a special constraint which indicates a unique identifier for each row

Take a few minutes to research the other rows.

Load The Schema

Load the schema into your database from the command line...

$ psql -d library < schema.sql

This command is also run from your Zsh prompt -- not inside psql

Loading A Seed File

We've provided a sql file that adds sample data into our library database.

Load that in so we can practice interacting with our data. Make sure to also look at its contents and see how authors and books are related.

$ psql -d library < seed.sql

Performing CRUD actions with SQL

CRUD stands for the most basic interactions we want to have with any database: Create, Read, Update and Destroy.

The most common SQL commands correspond to these 4 actions...

• INSERT -> Create a row
• SELECT -> Read / get information for rows
• UPDATE -> Update a row
• DELETE -> Destroy a row

First, enter into the library DB...

$ psql
$ \c library

INSERT

INSERT adds a row to a table...

INSERT INTO authors(name, nationality, birth_year) VALUES ('Adam Bray', 'United States of America', 1985);

SELECT

SELECT returns rows from a table...

-- select all columns from all rows
SELECT * FROM authors;

-- select only some columns, from all rows
SELECT name, birth_year FROM authors;

-- select rows that meet certain criteria
SELECT * FROM authors WHERE name = 'James Baldwin';

UPDATE

UPDATE updates values for one or more rows...

UPDATE authors SET name = 'Adam B.', birth_year = 1986 WHERE name = 'Adam Bray';

DELETE

DELETE removes rows from a table...

DELETE FROM authors WHERE name = 'Adam B.';

End of You Do: Building Our Database

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Exercises

There is one exercise:

• Basic Queries - SELECT, INSERT, UPDATE, DELETE

Resources

• SQL Cheatsheet