sql/

README

SQL-like Databases

Although there is a good bit of hype around interesting NoSQL databases and key/values stores, SQL-like databases are still ubiquitous. You can access, query, and otherwise interact with such databases via the databases/sql package in Go stdlib. There are a variety of libraries for databases/sql that allow you to connect to MySQL, Postgres, etc. In the following, we will be using a Postgres database hosted by ElephantSQL to illustrate database/sql functionality.

Get a Postgres server

• Create an account on ElephantSQL.
• Create a free "tiny turtle" instance.
• Get the URL from the details page of your "tiny turtle" instance.
• Export this URL to a environmental variable PGURL.
• Install the psql CLI tool.

Notes

• A sql.DB value is not a database connection.
• Using the sql.DB value, databases/sql (i) opens and closes connections to the actual underlying database, via the specified driver, and (ii) manages a pool of connections as needed.
• If you fail to release connections, you can cause databases/sql to open a lot of connections.
• After creating a sql.DB value, you can use it to query the database, execute statements, and commit transactions.
• When you iterate over rows and scan them into variables, Go performs data type conversions behind the scenes.

Links

Go database/sql tutorial
Common Go pitfalls when working with database/sql

Code Review

Open a database, ping the connection
Load data into a database
Retrieve data from a database
Modify data in a database

Exercises

Exercise 1

Query data/iris.db returning the sum of values in each of the sepal length, sepal width, petal length, and petal width columns grouped by species. Output the results to standard out.

Template | Answer

Exercise 2

Remove any rows in data/iris.db with sepal_length greater than 6.0.

Template | Answer

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All material is licensed under the Apache License Version 2.0, January 2004.