SQL

SQL is how you talk to relational databases. It's a programming language (although some would debate this) that lets you read, write, and update data, but also more, like add users, create functions, and other fun database admin tasks. Popular relational databases like PostgreSQL and MySQL unsurprisingly run on SQL.

A typical SQL statement might look like this:

SELECT 
    first_name,
    last_name,
    address,
    last_order_date
FROM users
WHERE signup_date > '2019-01-01'

SQL is pretty human readable – even if you don’t know it, you can guess what we’re doing here – and it’s a really useful thing for everyone to know, even if you’re not en engineer.