Databases + SQL

Lecture 9

Dr. Benjamin Soltoff

Cornell University
INFO 5001 - Fall 2025

September 23, 2025

Announcements

Announcements

• Homework 03
• Group project team survey due by end of tomorrow
• Quiz 01 on Friday

Learning objectives

• Introduce databases as a structure for data storage
• Introduce structured query language (SQL)
• Define database management systems (DBMS) and their variations
• Connect to an in-process database
• Execute database queries using {dbplyr} and SQL

Reading data into R

• Local data files
• Databases
• Web scraping
• Application programming interfaces (APIs)

Databases

• Large volumes of data lives in databases
• Rather than retrieving snapshots of databases to periodically analyze, better to query the database directly
• Structured Query Language

Database basics

Data is organized in tables

Major differences from data frames

• Stored on disk
• Tables are indexed
• Row-oriented structure for collecting data

Running databases

Databases run on database management systems (DBMS’s)

• Client-server
  • PostgreSQL, MariaDB, SQL Server
• Cloud
  • Snowflake, Amazon’s RedShift, and Google’s BigQuery
• In-process
  • SQLite or DuckDB

Intended benefits

• Centralized data storage
• Controlled access
• Unconstrained by system memory
• Faster queries

SQL queries and {dplyr} equivalents

SQL	{dplyr}
SELECT	select(), mutate(), rename(), relocate(), summarize()
FROM	N/A
GROUP BY	group_by()
WHERE	filter()
ORDER BY	arrange()

Relevant R packages

Objective: make interacting with databases as seamless as possible

• Front-end to DBMS - {DBI}
• Back-end to DBMS
  • {duckdb}
  • {odbc}
  • {RPostgres}
  • {RSQLite}
• Database backend for {dplyr} - {dbplyr}

Application exercise

ae-07

Note

• Go to the course GitHub org and find your ae-07 (repo name will be suffixed with your GitHub name).
• Clone the repo in Positron, run renv::restore() to install the required packages, open the Quarto document in the repo, and follow along and complete the exercises.
• Render, commit, and push your edits by the AE deadline – end of the day

Wrap up

Recap

• Databases are used to structure large data sets
• Use DBMS and {DBI} to connected to databases using R
• {dbplyr} translates common data tidying and wrangling tasks to SQL