Fix BigQuery Percentile and Median expressions not using correct backtick quoting (#17979)

 Fix BigQuery Percentile and Median expressions not using correct backtick quoting

Ensure the identifier components are quoted by reifying `ToSql` for the `APPROX_QUANTILES` expression

Add test to ensure query is created properly

Mark `:percentile-aggregations` as being supported in the new driver

modules/drivers/bigquery-cloud-sdk/src/metabase/driver/bigquery_cloud_sdk.clj

@@ -286,7 +286,7 @@
 ;;; |                                           Other Driver Method Impls                                            |
 ;;; +----------------------------------------------------------------------------------------------------------------+
 
-(defmethod driver/supports? [:bigquery-cloud-sdk :percentile-aggregations] [_ _] false)
+(defmethod driver/supports? [:bigquery-cloud-sdk :percentile-aggregations] [_ _] true)
 
 (defmethod driver/supports? [:bigquery-cloud-sdk :expressions] [_ _] true)
 

modules/drivers/bigquery-cloud-sdk/src/metabase/driver/bigquery_cloud_sdk/query_processor.clj

@@ -23,6 +23,7 @@
             [metabase.util.date-2 :as u.date]
             [metabase.util.honeysql-extensions :as hx]
             [metabase.util.i18n :refer [tru]]
+            [pretty.core :refer [PrettyPrintable]]
             [schema.core :as s]
             [toucan.db :as db])
   (:import [com.google.cloud.bigquery Field$Mode FieldValue]
@@ -415,13 +416,26 @@
       [(Math/round x) (Math/round (Math/pow 10 power))]
       (recur (* 10 x) (inc power)))))
 
+(defn- approx-quantiles
+  "HoneySQL form for the APPROX_QUANTILES invocation. The [OFFSET(...)] part after the function call is odd and
+  needs special treatment."
+  [driver expr offset quantiles]
+  (let [expr-hsql (sql.qp/->honeysql driver expr)]
+    (reify
+      hformat/ToSql
+      (to-sql [_]
+        (format "APPROX_QUANTILES(%s, %s)[OFFSET(%s)]"
+          (hformat/to-sql expr-hsql)
+          quantiles
+          offset))
+      PrettyPrintable
+      (pretty [_]
+        (format "APPROX_QUANTILES(%s, %s)[OFFSET(%s)]" (pr-str expr) (pr-str quantiles) (pr-str offset))))))
+
 (defmethod sql.qp/->honeysql [:bigquery-cloud-sdk :percentile]
   [driver [_ arg p]]
   (let [[offset quantiles] (percentile->quantile p)]
-    (hsql/raw (format "APPROX_QUANTILES(%s, %s)[OFFSET(%s)]"
-                      (hformat/to-sql (sql.qp/->honeysql driver arg))
-                      quantiles
-                      offset))))
+    (approx-quantiles driver arg offset quantiles)))
 
 (defmethod sql.qp/->honeysql [:bigquery-cloud-sdk :median]
   [driver [_ arg]]

modules/drivers/bigquery-cloud-sdk/test/metabase/driver/bigquery_cloud_sdk/query_processor_test.clj

@@ -821,3 +821,18 @@
                  :source-query {:source-table (mt/id :checkins)
                                 :aggregation  [[:count]]
                                 :breakout     [!month.date]}})))))))
+
+(deftest custom-expression-args-quoted
+  (mt/test-driver :bigquery-cloud-sdk
+    (mt/dataset sample-dataset
+      (testing "Arguments to custom aggregation expression functions have backticks applied properly"
+        (is (= {:mbql?      true
+                :params     nil
+                :table-name "orders"
+                :query      (str "SELECT APPROX_QUANTILES(`v3_sample_dataset.orders`.`quantity`, 10)[OFFSET(5)] AS `CE`"
+                                 " FROM `v3_sample_dataset.orders` LIMIT 10")}
+              (qp/query->native (mt/mbql-query orders
+                                  {:aggregation [[:aggregation-options
+                                                  [:percentile $orders.quantity 0.5]
+                                                  {:name "CE", :display-name "CE"}]]
+                                   :limit       10}))))))))