Show HN: GoSQL – A query engine in 319 LoC

81 points by archiewood 8 months ago | 9 comments
I've always been curious about how SQL engines actually work.

So I built a minimum viable SQL engine in Go.

- Supports CSV files as tables

- Supports SELECT, FROM, WHERE, LIMIT

It's very simple:

1. Parses query string

2. Converts it into an AST representation

3. Executes the query against the CSV

4. Returns the results

  • stevekemp 8 months ago
    Nice job.

    You can see this post for the start of a guide in implementing something very similar "Writing a SQL database from scratch in Go":

    https://notes.eatonphil.com/database-basics.html

    (Use the tag "sql" to find the later parts. Sadly not linked directly from that first one.)

    • eatonphil 8 months ago
      Thanks for mentioning! One of the most fun parts of this series I think is handling indexes on INSERT and actually making use of them based on (effectively) pattern matching on WHERE clauses.

      > (Use the tag "sql" to find the later parts. Sadly not linked directly from that first one.)

      There's a "Note" section right below that title that links to the other posts. :) I guess it is UX feedback that this was not obvious to spot.

      • archiewood 8 months ago
        Wow this is much more complete than mine, kudos.
    • iamcreasy 8 months ago
      Nice. I also wanted to know the details behind database engine and ACID compliance. So, decided to follow Database Design and Implementation by Edward Sciore, and re-implemented the database in Python: https://github.com/quazi-irfan/pySimpleDB

      This db treats file as raw disk and reads and writes in blocks. In the book, your step 3 and 4 will be a start of a transaction that uses recovery manager to log changes introduced by the query, and buffer manager to page in and out file blocks in memory. This book uses serializable isolation, so if buffer pool is full and can't page in new block or if another transactions are writing to that same block - the newer transaction will be rolled back after a brief wait.

      • lainga 8 months ago
        Try this talk about sqlite!

        https://www.youtube.com/watch?v=ZSKLA81tBis

        • zh2408 8 months ago
          Feel like you can achieve something similar in duckdb? duckdb allows you to query local csv, parquet, and even remote ones?
          • archiewood 8 months ago
            Oh definitely, I love DuckDB.

            This was a learning exercise for me as much as anything

          • coredog64 8 months ago
            This is very handy given the recent de-emphasizing of S3 Select by AWS.
            • ddmf 8 months ago
              Nice one, thanks, I'll have a look through this.
              • 8 months ago