Add implied grouping for project/let

Author: wotbrew

src/com/wotbrew/cinq/plan.clj

@@ -235,6 +235,14 @@
 
     _ (throw (ex-info "Not sure how to get columns from ra" {:ra ra}))))
 
+(defn grouped? [ra]
+  (boolean (some #{%count-sym} (columns ra))))
+
+(def aggregate-keywords
+  #{::count ::max ::min ::avg ::sum})
+
+(defn uses-aggregate? [expr] (boolean (some aggregate-keywords (tree-seq seqable? seq expr))))
+
 (defn dependent-cols* [cmap expr]
   (let [dmap (atom {})]
     ((fn ! [expr]
@@ -1025,8 +1033,23 @@
       r/attempt
       r/top-down))
 
+(def imply-grouping
+  (-> (r/match
+        (m/and [::project ?ra ?bindings]
+               (m/guard (some (fn [[_ expr]] (uses-aggregate? expr)) ?bindings))
+               (m/guard (not (grouped? ?ra))))
+        [::project [::group-by ?ra []] ?bindings]
+
+        (m/and [::let ?ra ?bindings]
+               (m/guard (some (fn [[_ expr]] (uses-aggregate? expr)) ?bindings))
+               (m/guard (not (grouped? ?ra))))
+        [::let [::group-by ?ra []] ?bindings])
+      r/attempt
+      r/top-down))
+
 (defn rewrite [ra]
   (-> ra
+      imply-grouping
       unique-ify-sub-queries
       unique-ify
       rewrite-sub-queries

test/com/wotbrew/cinq/implicit_group_test.clj

@@ -0,0 +1,14 @@
+(ns com.wotbrew.cinq.implicit-group-test
+  (:require [clojure.test :refer :all]
+            [com.wotbrew.cinq :as c]))
+
+(deftest groups-are-added-for-top-level-project-test
+  (is (= [4] (vec (c/q [a [1 2 3 4]] (c/count)))))
+  (is (= [3] (vec (c/q [a [1 2 3 nil]] (c/count a)))))
+  (is (= [3] (vec (c/q [a [1 2]] (c/sum a)))))
+  (is (= [1] (vec (c/q [a [2 1]] (c/min a)))))
+  (is (= [2] (vec (c/q [a [1 2]] (c/max a)))))
+  (is (= [3/2] (vec (c/q [a [1 2]] (c/avg a))))))
+
+(deftest groups-added-to-let-test
+  (is (= [1] (vec (c/q [a [] :let [n (+ 1 (c/count))]] n)))))

todo.txt

@@ -42,14 +42,6 @@ Like create-index, these functions create and return an index. In the case of fo
 
 ---
 
-Implicit group
-
-(q [f foo] (c/count))
-
-if let/proj/where/join/scan-src/group-expr/order-expr expr expects grouping, add it if is not already present
-
----
-
 Spilling
 
 spilled merge join