6.2.8 Aliases
Aliases are Snooze’s mechanism for letting you to refer to individual instances of an entity or expression within a query.
You can introduce aliases for entities, attributes or expressions using the following forms (see below for examples):
Introduces an alias for expr using the same scoping
rules as define.
Like define-alias but uses the same scoping rules as
let.
6.2.8.1 Entity aliases
It is sometimes necessary to refer to more than one instance of an entity within a query. Snooze lets you do this by defining aliases for entities. For example:
| (define-alias father person) |
| ; Luke's father: |
| (find-one |
| (sql (select #:what father |
| #:from (inner person |
| father |
| (= person.father-id father.id)) |
| #:where (= person.name "Luke")))) |
6.2.8.2 Attribute and expression aliases
It is sometimes useful to assign an alias to an attribute or expression.
For example, if you are #:ordering on an expression, SQL 97 requires you to add the same expression to your #:what clause. The only way to do this is to alias the expression:
| ; All people and BMIs, ordered by BMI: |
| (let-alias ([bmi (/ person.weight person.height)]) |
| (find-all |
| (sql (select #:what (person bmi) |
| #:from person |
| #:order ((asc bmi)))))) |