query: add #:distinct-on to select

Author: Bogdanp

deta-doc/deta.scrbl

@@ -913,8 +913,10 @@ queries.
   ((select _ maybe-distinct q-expr ...+)
    (select query maybe-distinct q-expr ...+))
   #:grammar
-  [(maybe-distinct (code:line)
-                   #:distinct)]
+  [(maybe-distinct
+    (code:line)
+    (code:line #:distinct)
+    (code:line #:distinct-on (q-expr ...+)))]
   #:contracts
   ([query query?])]{
 

deta-lib/info.rkt

@@ -1,7 +1,7 @@
 #lang info
 
 (define license 'BSD-3-Clause)
-(define version "0.18")
+(define version "0.19")
 (define collection "deta")
 
 (define deps '("base"

deta-lib/private/dialect/standard.rkt

@@ -240,7 +240,11 @@
     [(select distinct? columns from where group-by union order-by offset limit)
      (write-string "SELECT ")
      (when distinct?
-       (write-string "DISTINCT "))
+       (write-string "DISTINCT ")
+       (when (pair? distinct?)
+         (write-string "ON (")
+         (write/sep distinct? write-expr)
+         (write-string ") ")))
      (cond
        [(null? columns) (write-string "*")]
        [else            (write-stmt columns)])

deta-lib/private/query.rkt

@@ -100,7 +100,7 @@
   [returning (-> query? ast:expr? ast:expr? ... query?)]
   [select
    (->* [query? ast:expr?]
-        [#:distinct? boolean?]
+        [#:distinct? (or/c boolean? list?)]
         #:rest (listof ast:expr?)
         query?)]
   [select-for-schema

deta-lib/query.rkt

@@ -370,7 +370,6 @@
   (define (syntax->column-reference stx)
     (match-define (list _ a b)
       (regexp-match column-reference-re (symbol->string (syntax->datum stx))))
-
     (cons (datum->syntax stx a)
           (datum->syntax stx (id->column-name b))))
 
@@ -571,9 +570,14 @@
 
   (syntax-parse stx
     [(_ q:from-expr
-        (~alt (~optional (~and #:distinct distinct))) ...
+        (~alt (~optional (~and #:distinct distinct))
+              (~optional (~seq #:distinct-on (distinct-expr:q-expr ...+)))) ...
         e:q-expr ...+)
-     #:with distinct? (if (attribute distinct) #'#t #'#f)
+     #:with distinct?
+     (cond
+       [(attribute distinct-expr) #'(list distinct-expr.e ...)]
+       [(attribute distinct) #'#t]
+       [else #'#f])
      #'(dyn:select
         #:distinct? distinct?
         q.e e.e ...)]))

deta-test/deta/sql-postgresql.rkt

@@ -247,6 +247,14 @@
            (select #:distinct t.name t.count))
        "SELECT DISTINCT t.name, t.\"count\" FROM tags AS t"))
 
+    (test-case "suppports DISTINCT ON in from-queries"
+      (check-emitted
+       (~> (from "actions" #:as a)
+           (select #:distinct-on (a.agent-id) a.agent-id a.action)
+           (order-by ([a.agent-id]
+                      [a.created-at #:desc])))
+       "SELECT DISTINCT ON (a.agent_id) a.agent_id, a.\"action\" FROM actions AS a ORDER BY a.agent_id, a.created_at DESC"))
+
     (test-case "supports COND as an alias for CASE"
       (check-emitted
        (select