Implement CREATE INDEX

doc/clause-reference.md

@@ -98,7 +98,7 @@ names: the "from" and the "to" names.
 
 > Note: `:modify-column` is MySQL-specific and should be considered legacy and deprecated. `:alter-column` will produce `MODIFY COLUMN` when the MySQL dialect is selected.
 
-### add-index, drop-index
+### add-index, drop-index, create-index
 
 Used with `:alter-table`,
 `:add-index` accepts a single (function) expression
@@ -125,6 +125,22 @@ user=> (-> (h/alter-table :fruit)
 ["ALTER TABLE fruit ADD PRIMARY KEY(id)"]
 ```
 
+Some databases treat the standalone `:create-index` differently (e.g. PostgreSQL) while some treat it as an alias to `:alter-table` `:add-index` (e.g. MySQL). It accepts a pair of index specification and column specification:
+
+```clojure
+user=> (sql/format {:create-index [:my-idx [:fruit :appearance]]})
+["CREATE INDEX my_idx ON fruit (appearance)"]
+user=> (sql/format {:create-index [[:unique :another-idx] [:fruit :color :appearance]]})
+["CREATE UNIQUE INDEX another_idx ON fruit (color, appearance)"]
+```
+
+PostgreSQL supports IF NOT EXISTS and expressions instead of columns. This may make `:create-index` more useful than `:add-index`:
+
+```clojure
+user=> (sql/format (h/create-index [:unique :another-idx :if-not-exists] [:fruit :color :%lower.appearance]))
+["CREATE UNIQUE INDEX IF NOT EXISTS another_idx ON fruit (color, LOWER(appearance))"]
+```
+
 ### rename-table
 
 Used with `:alter-table`,

src/honey/sql.cljc

@@ -51,6 +51,7 @@
    :create-extension
    :drop-table :drop-view :drop-materialized-view :drop-extension
    :refresh-materialized-view
+   :create-index
    ;; then SQL clauses in priority order:
    :raw :nest :with :with-recursive :intersect :union :union-all :except :except-all
    :table
@@ -1255,6 +1256,17 @@
                                (into more)
                                (conj (when as (sql-kw as))))))]))
 
+(defn- format-create-index [k clauses]
+  (let [[index-spec [table & exprs]] clauses
+        [pre entity ine & more] (destructure-ddl-item index-spec (str (sql-kw k) " options"))
+        [sqls params] (format-expr-list exprs)]
+    (into [(str/join " " (remove empty?
+                                 (-> ["CREATE" pre "INDEX" ine entity
+                                      "ON" (format-entity table)
+                                      (str "(" (str/join ", " sqls) ")")]
+                                     (into more))))]
+          params)))
+
 (defn- format-with-data [_ data]
   (let [data (if (sequential? data) (first data) data)]
     [(str/join " " (remove nil?
@@ -1433,6 +1445,7 @@
          :drop-view       #'format-drop-items
          :drop-materialized-view #'format-drop-items
          :refresh-materialized-view (fn [_ x] (format-create :refresh :materialized-view x nil))
+         :create-index    #'format-create-index
          :raw             (fn [_ x] (raw-render x))
          :nest            (fn [_ x]
                             (let [[sql & params] (format-dsl x {:nested true})]

src/honey/sql/helpers.cljc

@@ -375,6 +375,20 @@
   [& views]
   (generic :refresh-materialized-view views))
 
+(defn create-index
+  "Accepts an index spexification and a column specification. The column
+  specification consists of table name and one or more columns.
+
+  (create-index :name-of-idx [:table :col])
+  (create-index :name-of-idx [:table :col1 :col2])
+  (create-index [:unique :name-of-idx] [:table :col])
+
+  PostgreSQL also supports :if-not-exists and expressions instead of columns.
+
+  (create-index [:name-of-idx :if-not-exists] [:table :%lower.col])"
+  [& args]
+  (generic :create-index args))
+
 (defn with
   "Accepts one or more CTE definitions.
 

test/honey/sql/helpers_test.cljc

@@ -7,6 +7,7 @@
             [honey.sql.helpers :as h
              :refer [add-column add-index alter-table columns create-table create-table-as create-view
                      create-materialized-view drop-view drop-materialized-view
+                     create-index
                      bulk-collect-into
                      cross-join do-update-set drop-column drop-index drop-table
                      filter from full-join
@@ -962,3 +963,21 @@
     (is (= '{}
            (-> '{}
                (where))))))
+
+(deftest test-create-index
+  (testing "create index, commonly supported features"
+    (is (= ["CREATE INDEX my_column_idx ON my_table (my_column)"]
+           (sql/format {:create-index [:my-column-idx [:my-table :my-column]]})))
+    (is (= ["CREATE INDEX my_column_idx ON my_table (my_column)"]
+           (sql/format (create-index :my-column-idx [:my-table :my-column]))))
+    (is (= ["CREATE UNIQUE INDEX my_column_idx ON my_table (my_column)"]
+           (sql/format (create-index [:unique :my-column-idx] [:my-table :my-column]))))
+    (is (= ["CREATE INDEX my_column_idx ON my_table (my_column, my_other_column)"]
+           (sql/format (create-index :my-column-idx [:my-table :my-column :my-other-column])))))
+  (testing "PostgreSQL extensions (IF NOT EXISTS and expressions)"
+    (is (= ["CREATE INDEX IF NOT EXISTS my_column_idx ON my_table (my_column)"]
+           (sql/format (create-index [:my-column-idx :if-not-exists] [:my-table :my-column]))))
+    (is (= ["CREATE UNIQUE INDEX IF NOT EXISTS my_column_idx ON my_table (my_column)"]
+           (sql/format (create-index [:unique :my-column-idx :if-not-exists] [:my-table :my-column]))))
+    (is (= ["CREATE INDEX my_column_idx ON my_table (LOWER(my_column))"]
+           (sql/format (create-index :my-column-idx [:my-table :%lower.my-column]))))))

test/honey/sql_test.cljc

@@ -1311,5 +1311,4 @@ ORDER BY id = ? DESC
 
 (comment
   ;; partial workaround for #407:
-  (sut/format {:select :f.* :from [[:foo [:f :for :system-time]]] :where [:= :f.id 1]})
-  )
+  (sut/format {:select :f.* :from [[:foo [:f :for :system-time]]] :where [:= :f.id 1]}))