From 2746c6b08b878190ee7c54a7414bf444c660ff1e Mon Sep 17 00:00:00 2001
From: Carlo Zancanaro <carlo@clearboxsystems.com.au>
Date: Mon, 25 Nov 2013 01:13:11 +1100
Subject: Add a 'distinct' operator - still a bug to fix on renaming

---
 src/clojure_sql/compiler.clj |  4 +++-
 src/clojure_sql/core.clj     | 10 +++++++++-
 src/clojure_sql/dsl.clj      | 11 ++++++++++-
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/clojure_sql/compiler.clj b/src/clojure_sql/compiler.clj
index 50c14af..828da64 100644
--- a/src/clojure_sql/compiler.clj
+++ b/src/clojure_sql/compiler.clj
@@ -225,7 +225,7 @@
 (def ^:private set-operations {:union "UNION", :intersect "INTERSECT"})
 
 (defmulti compile-query (fn [db _] db) :default :postgres)
-(defmethod compile-query :postgres [db {:keys [tables fields joins where sort group having take drop set-operation queries]}]
+(defmethod compile-query :postgres [db {:keys [tables fields joins where sort group having take drop distinct set-operation queries]}]
   (or (if set-operation
         (let [op-str (str ") " (get set-operations set-operation) " (")]
           (->> queries
@@ -234,6 +234,8 @@
                ((p-lift string/join op-str))
                $add-parentheses)))
       ($str (return "SELECT ")
+            (return (if distinct
+                      "DISTINCT "))
             (compile-fields db fields)
             (if tables
               ($str (return " FROM ")
diff --git a/src/clojure_sql/core.clj b/src/clojure_sql/core.clj
index 415c7f4..613adf6 100644
--- a/src/clojure_sql/core.clj
+++ b/src/clojure_sql/core.clj
@@ -17,7 +17,7 @@
 
 (pull clojure-sql.dsl
       table join
-      project rename
+      project rename distinct
       prefix-names-matching prefix-names as-subobject
       select
       group
@@ -63,3 +63,11 @@
   [query]
   (assert (:executor query) "Cannot execute a query without a query executor")
   (q/delete! (:executor query) query))
+
+(join (-> (table :x)
+          (project [:a :b]))
+      (-> (table :x)
+          (project [:a :b])
+          distinct))
+
+
diff --git a/src/clojure_sql/dsl.clj b/src/clojure_sql/dsl.clj
index 2a22eea..5c804d2 100644
--- a/src/clojure_sql/dsl.clj
+++ b/src/clojure_sql/dsl.clj
@@ -69,7 +69,6 @@
   (throw (ex-info "Cannot union queries with different fields"
                   {:queries queries})))
 
-
 (defn ^:private rename-table [query from to]
   (q/map->Query (walk/prewalk-replace {from to} (into {} query))))
 
@@ -201,6 +200,7 @@
        (nil? (:having query))
        (nil? (:take query))
        (nil? (:drop query))
+       (nil? (:distinct query))
        (nil? (:set-operation query))))
 
 (defn ^:private convert-to-subquery [query]
@@ -214,6 +214,7 @@
   (cond (joinable? query) query
         (:take query) (convert-to-subquery query)
         (:drop query) (convert-to-subquery query)
+        (:distinct query) (convert-to-subquery query)
         :else (convert-to-subquery (remove-sort query))))
 
 (defn ^:private rename-all-tables [query]
@@ -393,6 +394,14 @@
       (assoc query :drop (+ old-drop n))
       (assoc query :drop n))))
 
+(defn distinct
+  "Return only unique rows from this query."
+  [query]
+  (assoc (if (or (:take query) (:drop query))
+           (convert-to-subquery query)
+           query)
+    :distinct true))
+
 (defn ^:private union-compatible? [& queries]
   (and (every? (comp seq keys :fields) queries)
        (apply = (map (comp set keys :fields) queries))
-- 
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