The Structured (English) Query Language
This is just a small observation about one counterintuitive feature of the SQL language.
SQL (Structured Query Language) was initially named SEQUEL (Structured English Query Language). One word clearly explains why the “keyed-in” SQL statements order is different than the logical query processing order.
Say, we’d like to ask someone for a bottle of beer from a fridge. The first thing we think about is what do we want (a beer) and only then how to get it (from the fridge).
In English, we’d say:
Give me a bottle of beer from the fridge, please.
First, what do we want, second, how to get it.
But if we wrote a program, we want to make an algorithm: first — how, second — what:
Open the fridge, take a bottle of beer.
The so-called “keyed-in order” of a standard SQL query is:
But the logical query processing order is different:
This is why we can’t, for example, refer in the
WHERE clause to a column alias defined in the
SELECT clause. This isn't allowed because the
WHERE clause is evaluated before the
Now take a classic SQL query:
And compare to it’s LINQ-expression equivalent:
select at the last line looks more natural, isn't it?
orderby goes before the
select, but this is exactly how it is processed in the LINQ code: