Fixes #328 by adding :distinct special syntax

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changes
 
 * 2.0.next in progress
+  * Fix #328 by adding `:distinct` as special syntax, affecting an expression.
   * Support PostgreSQL's `&&` array operator.
   * Clarify how to `SELECT` a function expression (in **Getting Started**).
 

doc/special-syntax.md

@@ -60,6 +60,15 @@ expression (comma-separated, wrapped in parentheses):
 ;;=> ["(a, b, ?, x + ?)" "red" 1]
 ```
 
+## distinct
+
+Accepts a single expression and prefixes it with `DISTINCT `:
+
+```clojure
+(sql/format {:select [ [[:count [:distinct :status]] :n] ] :from :table})
+;;=> ["SELECT COUNT(DISTINCT status) AS n FROM table"]
+```
+
 ## entity
 
 Accepts a single keyword or symbol argument and produces a

src/honey/sql.cljc

@@ -1074,6 +1074,10 @@
     (fn [_ [& args]]
       (let [[sqls params] (format-expr-list args)]
         (into [(str "(" (str/join ", " sqls) ")")] params)))
+    :distinct
+    (fn [_ [x]]
+      (let [[sql & params] (format-expr x {:nested true})]
+        (into [(str "DISTINCT " sql)] params)))
     :escape
     (fn [_ [pattern escape-chars]]
       (let [[sql-p & params-p] (format-expr pattern)