For me, it's the lack of SQLs expression composability. And yes, I'm well aware of various libraries and plug-ins that purport to yield "composable SQL". It's never gonna' happen at-scale due to decades of investment in query optimizers for the popular relational engines.
Just make peace with all of SQL's warts or go NoSQL and make piece with code-bloat and eventual consistency.
After discovering the truth, it was interesting to find out that almost everyone I knew who wasn't a snr db engineer shared the same incorrect assumption.
>Imagine a programming language without functions. You can only write code that operates on concrete values, i.e. variables or literals. So instead of writing a function and calling it anywhere you have to write these little code templates as comments and every time you want to “call” the “function” you copy the template and do a search/replace.
>This would be tiresome. But that’s what SQL is. The concrete values are the table names. The code is the queries. And the function templates you have to search replace are your business logic, which must be inlined everywhere it is used.