Adds support for except set operation #254

README.md

@@ -295,9 +295,9 @@ If you want to delete everything from a table, you can use `truncate`:
 => ["TRUNCATE films"]
 ```
 
-### Unions
+### Set operations
 
-Queries may be united within a :union or :union-all keyword:
+Queries may be combined within a :union, :union-all, :intersect or :except keyword:
 
 ```clojure
 (sql/format {:union [(-> (select :*) (from :foo))

src/honeysql/format.cljc

@@ -226,6 +226,7 @@
    :intersect 35
    :union 40
    :union-all 45
+   :except 47
    :select 50
    :insert-into 60
    :update 70
@@ -686,6 +687,10 @@
   (binding [*subquery?* false]
     (string/join " INTERSECT " (map to-sql maps))))
 
+(defmethod format-clause :except [[_ maps] _]
+  (binding [*subquery?* false]
+    (string/join " EXCEPT " (map to-sql maps))))
+
 (defmethod fn-handler "case" [_ & clauses]
   (str "CASE "
        (space-join

src/honeysql/helpers.cljc

@@ -345,3 +345,6 @@
 
 (defmethod build-clause :intersect [_ m maps]
   (assoc m :intersect maps))
+
+(defmethod build-clause :except [_ m maps]
+  (assoc m :except maps))

test/honeysql/format_test.cljc

@@ -126,6 +126,11 @@
                               {:select [:foo] :from [:bar2]}]})
          ["SELECT foo FROM bar1 INTERSECT SELECT foo FROM bar2"])))
 
+(deftest except-test
+  (is (= (format {:except [{:select [:foo] :from [:bar1]}
+                           {:select [:foo] :from [:bar2]}]})
+         ["SELECT foo FROM bar1 EXCEPT SELECT foo FROM bar2"])))
+
 (deftest inner-parts-test
   (testing "The correct way to apply ORDER BY to various parts of a UNION"
     (is (= (format