6.2.2 The #:what clause

The #:what clause specifies the result type of the query. The data in the #:what clause must be derived from that selected in the #:from clause.

For example, the query:

  (sql (select #:from person))

has a result type of person, whereas the query:

  (sql (select #:what person.name #:from person))

has a result type of string. The expression:

  (find-all (sql (select #:what person.name #:from person)))

would therefore return a (listof person).

The #:what clause can be one of the following:

• an entity or entity alias:

  ; (listof person)

  (find-all

  (sql (select #:what person

  #:from ; ...)))

• an attribute or attribute alias:

  ; (listof string)

  (find-all

  (sql (select #:what person.surname

  #:from ; ...)))

• The #:where clause

  an SQL expression (like those used in #:where clauses):

  ; (listof string)

  (find-all

  (sql (select #:what (string-append

  person.forenames

  " "

  person.surname)

  #:from ; ...)))

• a list of the above:

  ; (listof (list string string))

  (find-all

  (sql (select #:what (person.forenames person.surname)

  #:from ; ...)))

If the #:what clause is omitted, Snooze infers the result type from the #:from clause:

• if #:from is a single entity, the result type is the relevant persistent struct type:

  ; (listof person)

  (find-all

  (sql (select #:from person)))

• if #:from is a subquery, the result type is the same as that of the subquery:

  ; (listof person)

  (find-all

  (sql (select #:from (select #:from person))))

• if #:from is a join, the result type is a flattened list of the result types of the join arguments:

  ; (listof (list employer employee))

  (find-all

  (sql (select #:from (inner employer

  employee

  ; ...))))