6.2.5 #:group and #:having clauses

GROUP in PostgreSQL

SQL provides a mechanism for grouping and filtering the results of queries that involve aggregate functions. The semantics are confusing, unintuitive, and outside the scope of this document. Snooze provides access to these features (for hardier programmers) via the #:group and #:having clauses:

The #:group clause is a list of #:what items by which results should be grouped. For example:

  ; (listof (list employer natural-number))
  ; The number of employees working for each employer.
  (find-all
   (sql (select #:what  (employer (count employee.id))
                #:from  (inner employer
                               employee
                               ; ...)
                #:group (employer))))

The #:having clause is like the #:where clause but eliminates groups from the query results.

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1	Quick start
2	Snooze modules
3	Persistent structures
4	Entities, relationships and attributes
5	Connecting to, querying and updating databases
6	Queries
7	Quick find procedures
8	Acknowledgements

6.1	Query methods/ procedures
6.2	Query syntax

6.2.1	Data sources, result types and the #: from clause
6.2.2	The #: what clause
6.2.3	The #: where clause
6.2.4	The #: order clause
6.2.5	#: group and #: having clauses
6.2.6	#: limit and #: offset clauses
6.2.7	The #: distinct clause
6.2.8	Aliases
6.2.9	Procedural query layer