Sec.1-Ch.2-Subsec.9：Running SQL in R
How to Use SQL Queries on R Data Frames to Boost Your Data Analysis Workflow
In medical statistics and clinical research, data handling and analysis often involve large tables and complex calculations. R is a go-to tool for statistical analysis, offering powerful ways to manipulate data. But for users familiar with SQL, R’s native data manipulation tools like dplyr or data.table—though powerful—can feel less intuitive than SQL’s straightforward syntax.
That’s where the sqldf package comes in. It lets you run SQL statements directly on R data frames, combining the strengths of R and SQL. In this article, we’ll dive into how sqldf works, the database backends it supports, and its applications in medical statistics.
1. R and SQL Databases
1.1 Understanding SQL Databases
SQL (Structured Query Language) is a domain-specific language designed for managing relational databases. It’s excellent for handling structured data—data organized into tables with relationships—and provides robust data management features.
SQL dates back to the early 1970s. IBM researchers Donald D. Chamberlin and Raymond F. Boyce were inspired by Edgar F. Codd’s relational model and started developing SQL at IBM’s San Jose research lab. Originally, it was called SEQUEL (Structured English Query Language), created to work with IBM’s System R prototype relational database. Due to a trademark issue, it was renamed SQL, short for Structured Query Language.
Key milestones in SQL history:
Mid-1970s: IBM successfully tested SQL on System R, proving its practicality.
1979: IBM released its first commercial SQL products, including System/38, SQL/DS, and IBM Db2.
June 1979: Oracle (originally Relational Software, Inc.) launched the first commercial SQL implementation, Oracle V2, running on VAX computers—marking SQL’s commercial debut.
1986: SQL became an ANSI standard in the U.S.
1987: ISO adopted SQL as an international standard.
Subsequent versions: The SQL standard has evolved over time, with major updates in 1989, 1992, 1999, 2003, 2006, 2011, 2016, and 2023, gradually adding more features and database capabilities.
Today, SQL is a standard declarative language (4GL), covering:
