The idea is nice, but it seems like the text is not explaining much. If you don't have a background in parser writing you have no clue what types are defined there and why in the very first code block. If you're not an SQL expert you might still know what SELECT and WHERE is, but do you think everybody knows what's an INTO keyword is used for? Where does the lex function come from? Why do I have a lexer and a lex()? Where does the cursor come from that I give into it? Why don't I give it a string? My user input SQL statement is a string, right? Why does the lex function have two for loops? What can't be done in one? Does this whole logic actually have a name maybe? What other alternatives to parsing SQL are out there? Why choose this path?

All that knowledge can't be gathered by just staring at the source code. And for people who understand the source code well enough to gather all this info themselves maybe they don't need the blog post around it, right?

Now all this I don't say to demotivate you. I hope you're strong enough to get over negative feedback and think about rewriting it to something more useful. I see a lot of potential here. But every good writer needs one (or ten million hacker news reading) editors to get to the really good content.