SQL: Remove useless boolean CASTs in filters.

sql/src/main/java/io/druid/sql/calcite/expression/Expressions.java

@@ -218,9 +218,12 @@ public static DimFilter toFilter(
       final RexNode expression
   )
   {
-    if (expression.getKind() == SqlKind.AND
-        || expression.getKind() == SqlKind.OR
-        || expression.getKind() == SqlKind.NOT) {
+    if (expression.getKind() == SqlKind.CAST && expression.getType().getSqlTypeName() == SqlTypeName.BOOLEAN) {
+      // Calcite sometimes leaves errant, useless cast-to-booleans inside filters. Strip them and continue.
+      return toFilter(plannerContext, rowSignature, Iterables.getOnlyElement(((RexCall) expression).getOperands()));
+    } else if (expression.getKind() == SqlKind.AND
+               || expression.getKind() == SqlKind.OR
+               || expression.getKind() == SqlKind.NOT) {
       final List<DimFilter> filters = Lists.newArrayList();
       for (final RexNode rexNode : ((RexCall) expression).getOperands()) {
         final DimFilter nextFilter = toFilter(

sql/src/test/java/io/druid/sql/calcite/CalciteQueryTest.java

@@ -2965,6 +2965,34 @@ public void testCountStarWithTimeFilter() throws Exception
     );
   }
 
+  @Test
+  public void testRemoveUselessCaseWhen() throws Exception
+  {
+    testQuery(
+        "SELECT COUNT(*) FROM druid.foo\n"
+        + "WHERE\n"
+        + "  CASE\n"
+        + "    WHEN __time >= TIME_PARSE('2000-01-01 00:00:00', 'yyyy-MM-dd HH:mm:ss') AND __time < TIMESTAMP '2001-01-01 00:00:00'\n"
+        + "    THEN true\n"
+        + "    ELSE false\n"
+        + "  END\n"
+        + "OR\n"
+        + "  __time >= TIMESTAMP '2010-01-01 00:00:00' AND __time < TIMESTAMP '2011-01-01 00:00:00'",
+        ImmutableList.of(
+            Druids.newTimeseriesQueryBuilder()
+                  .dataSource(CalciteTests.DATASOURCE1)
+                  .intervals(QSS(Intervals.of("2000/2001"), Intervals.of("2010/2011")))
+                  .granularity(Granularities.ALL)
+                  .aggregators(AGGS(new CountAggregatorFactory("a0")))
+                  .context(TIMESERIES_CONTEXT_DEFAULT)
+                  .build()
+        ),
+        ImmutableList.of(
+            new Object[]{3L}
+        )
+    );
+  }
+
   @Test
   public void testCountStarWithTimeMillisecondFilters() throws Exception
   {