One of the big flaw of R is that data loaded into it are stored in the memory (on the RAM) and not on the disk. As you are working in an analysis with large (big) data the processing time of simple and more complex functions can become very long or even crash your computer. SQL enters here, it is a powerful language designed to work with (large) database and to perform simple operation (like subsetting, sorting …) on them. It is particularly useful to explore very large dataset and format the data for further analysis. There are many programs for doing database management using SQL. I decided to start looking at MySQL since it has an R package and is rather easy to set up (one could also use PostgreSQL …). In this post I will show you step by step how to create a database in MySQL, to upload data from R into it, then to do some queries to look at the power of SQL. Before I start note that the data.table package was developed to perform fast operation on big data (have a look here).
Create a database
First you need to download MySQL from this website or from synaptic for the ubuntu users. Then you need to open a shell window (type cmd for windows users, terminal for Linux), type this:
> mysql -p -u root
This will ask you for the password of the root user if it worked you will see some text and mysql> appearing. Then if you don’t want to bother with different users and their rights you can directly create a database using:
mysql> CREATE DATABASE intro_to_sql;
That’s it you created a database named intro_to_sql. At this point it is very important to remember that every time you are in the shell with mysql you need …read more
Source:: r-bloggers.com