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The DataSQRL SQL Primer

SQL (Structured Query Language) is the standard query language used by relational database systems.

SQRL is based on SQL and this documentation assumes basic familiarity with SQL for writing queries.

SQL Tutorials​

If you haven't used SQL before, we recommend that you follow ones of these tutorials until you feel comfortable writing SELECT .. FROM .. WHERE .. GROUP BY queries. The investment to learn SQL is going to pay off whether or not you are going to use DataSQRL.

  • SQLBolt: SQLBolt provides an interactive tutorial for SQL beginners. The tutorial is divided into several lessons that cover different SQL concepts. Each lesson includes a set of interactive exercises that allow users to practice SQL queries.

  • Khan Academy SQL Course: Khan Academy offers a free, self-paced SQL course that covers the basics of SQL syntax and querying data. The course includes interactive exercises to help reinforce the concepts learned.

  • W3Schools SQL Tutorial: W3Schools is a popular web development tutorial website that provides a comprehensive SQL tutorial. The tutorial includes explanations, examples, and exercises that cover basic and advanced SQL concepts.

We listed a number of tutorials we like. Pick one of those or choose your own. There are lots of great resources on SQL out there.

SQL Refresher​

SQRL uses SQL SELECT queries to define tables. A SELECT query has the structure:

SELECT columns FROM table JOIN otherTable ON joinCondition 
    WHERE filterCondition 
    GROUP BY groupingColumns
    ORDER BY orderColumn [ASC|DESC]
    LIMIT number;

In addition, the UNION ALL operator is used to combine data from multiple queries.

The column expression after SELECT and the conditions can include function calls to manipulate data and predicates in filters. Common SQL functions and predicates include:

  • Aggregation Functions: min, max, avg, count, and count distinct
  • Conditional Functions: case when, coalesce
  • Predicates: in, between

Time intervals are specified with the INTERVAL syntax, such as INTERVAL 5 DAY.

If all of the above looks familiar to you, you know enough SQL to learn SQRL quickly. Otherwise, we recommend you do a quick google search to refresh your memory or follow one of the tutorials above.