[CALCITE-6196] Accept BigQuery PERCENTILE functions without OVER clause

Address Mihai comment

Author: tanclary

core/src/main/java/org/apache/calcite/rel/core/AggregateCall.java

@@ -512,9 +512,8 @@ public Aggregate.AggCallBinding createBinding(
     final RelDataTypeFactory typeFactory =
         aggregateRelBase.getCluster().getTypeFactory();
 
-    if (aggFunction.getKind() == SqlKind.PERCENTILE_DISC
-        || aggFunction.getKind() == SqlKind.PERCENTILE_CONT) {
-      assert collation.getKeys().size() == 1;
+    if (this.argList.size() == 1 && (aggFunction.getKind() == SqlKind.PERCENTILE_DISC
+        || aggFunction.getKind() == SqlKind.PERCENTILE_CONT)) {
       return new Aggregate.PercentileDiscAggCallBinding(typeFactory,
           aggFunction, SqlTypeUtil.projectTypes(rowType, argList),
           SqlTypeUtil.projectTypes(rowType, collation.getKeys()).get(0),

core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java

@@ -871,7 +871,6 @@ static RelDataType deriveTypeSplit(SqlOperatorBinding operatorBinding,
               ReturnTypes.DOUBLE,
               OperandTypes.NUMERIC_UNIT_INTERVAL_NUMERIC_LITERAL)
           .withFunctionType(SqlFunctionCategory.SYSTEM)
-          .withOver(true)
           .withPercentile(true)
           .withAllowsNullTreatment(true)
           .withAllowsFraming(false);
@@ -886,7 +885,6 @@ static RelDataType deriveTypeSplit(SqlOperatorBinding operatorBinding,
               ReturnTypes.ARG0,
               OperandTypes.NUMERIC_UNIT_INTERVAL_NUMERIC_LITERAL)
           .withFunctionType(SqlFunctionCategory.SYSTEM)
-          .withOver(true)
           .withPercentile(true)
           .withAllowsNullTreatment(true)
           .withAllowsFraming(false);

core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorImpl.java

@@ -6561,7 +6561,7 @@ private SqlNode navigationInDefine(SqlNode node, String alpha) {
     // Because there are two forms of the PERCENTILE_CONT/PERCENTILE_DISC functions,
     // they are distinguished by their operand count and then validated accordingly.
     // For example, the standard single operand form requires group order while the
-    // 2-operand form allows for null treatment and requires an OVER() clause.
+    // 2-operand form allows for null treatment.
     if (op.isPercentile()) {
       switch (aggCall.operandCount()) {
       case 1:
@@ -6586,7 +6586,6 @@ private SqlNode navigationInDefine(SqlNode node, String alpha) {
         break;
       case 2:
         assert op.allowsNullTreatment();
-        assert op.requiresOver();
         assert op.requiresGroupOrder() == Optionality.FORBIDDEN;
         break;
       default:

core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java

@@ -1374,6 +1374,30 @@ private static String toSql(RelNode root, SqlDialect dialect,
         .withMysql().ok(expectedMysql);
   }
 
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-6196">[CALCITE-6196]
+   * Remove OVER requirement for BigQuery PERCENTILE_CONT/DISC</a>. */
+  @Test void testPercentileContFunctionWithoutOver() {
+    final String query = "select percentile_cont(\"product_id\", .5) "
+        + "from \"foodmart\".\"product\"";
+    final String expected = "SELECT PERCENTILE_CONT(product_id, 0.5)\n"
+        + "FROM foodmart.product";
+
+    sql(query).withBigQuery().withLibrary(SqlLibrary.BIG_QUERY).ok(expected);
+  }
+
+  /** Test case for
+   * <a href="https://issues.apache.org/jira/browse/CALCITE-6196">[CALCITE-6196]
+   * Remove OVER requirement for BigQuery PERCENTILE_CONT/DISC</a>. */
+  @Test void testPercentileDiscFunctionWithoutOver() {
+    final String query = "select percentile_disc(\"product_id\", .5) "
+        + "from \"foodmart\".\"product\"";
+    final String expected = "SELECT PERCENTILE_DISC(product_id, 0.5)\n"
+        + "FROM foodmart.product";
+
+    sql(query).withBigQuery().withLibrary(SqlLibrary.BIG_QUERY).ok(expected);
+  }
+
   /** As {@link #testSum0BecomesCoalesce()} but for windowed aggregates. */
   @Test void testWindowedSum0BecomesCoalesce() {
     final String query = "select\n"