If you want to believe that popularity is a measure or reliable indicator of quality, I can't be bothered with you.
PS I have a worked-out example on my site of what it takes to enforce a business rule "no one has a salary higher than his manager's" in SQL (> 100 LOC) and in SIRA_PRISE (one single relatively simple formula of the RA to declare). You decide which is "better".
However, there is a more insidious problem with SQL: it's all too easy to write SQL statements that have O(N^2) complexity. A simple JOIN can easily result in O(N^2) complexity, yet there aren't easy tools to identify these performance issues. As a result, as a database grows, things that once were executed quickly take forever.
I'd like to see the end of joins, replaced with something that is more explicit about what is happening under the hood.
However. You are wrong tying the problem to joins. I remember an analyst who launched a SELECT COUNT because he was just curious about the number of rows in the table. No joins involved but users did suffer. Elsewhere in this thread I've seen the problem be tied to table scans, and that's also wrong. A table scan isn't a problem if it's a 5-page table. As Darwen often argued : why are people always only lamenting about those couple of tables with millions of rows ? Why should we deprive users of the power of relational algebra if their database simply aren't that big ?
It's a matter of determining the cost of the data access strategy (regardless of JOIN/EXCEPT/what_have_you) and (implementing a protocol for) capping it at runtime (or earlier if possible). No need for language changes here.
I was using joins as the common example. Sure, there are many other ways of using SQL to shoot yourself in the foot, but most of the issues I've run into seem to come from joins.