diff --git a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
index 59404855601..d5514a7161a 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlDialect.java
@@ -447,6 +447,22 @@ public void unparseCall(SqlWriter writer, SqlCall call, int leftPrec,
       int rightPrec) {
     SqlOperator operator = call.getOperator();
     switch (call.getKind()) {
+    case IS_TRUE:
+    case IS_NOT_FALSE:
+    case IS_FALSE:
+    case IS_NOT_TRUE:
+      if (call.operand(0) instanceof SqlBasicCall
+          && !isOperandParensCandidate(writer, call.operand(0), operator)) {
+        // Wrap in parentheses the operand associated to any of the above functions
+        // if the operand is a SqlBasicCall and will not have parenthesis applied when unparsed
+        final SqlWriter.Frame frame = writer.startList("(", ")");
+        call.operand(0).unparse(writer, operator.getLeftPrec(), operator.getRightPrec());
+        writer.endList(frame);
+        writer.keyword(operator.getName());
+        break;
+      }
+      operator.unparse(writer, call, leftPrec, rightPrec);
+      break;
     case ROW:
       // Remove the ROW keyword if the dialect does not allow that.
       if (!getConformance().allowExplicitRowValueConstructor()) {
@@ -467,6 +483,13 @@ public void unparseCall(SqlWriter writer, SqlCall call, int leftPrec,
     }
   }
 
+  private boolean isOperandParensCandidate(SqlWriter writer, SqlBasicCall operand,
+      SqlOperator operator) {
+    return operator.getLeftPrec() > operand.getOperator().getLeftPrec()
+        || operator.getRightPrec() >= operand.getOperator().getRightPrec()
+        || writer.isAlwaysUseParentheses() && operand.isA(SqlKind.EXPRESSION);
+  }
+
   public void unparseDateTimeLiteral(SqlWriter writer,
       SqlAbstractDateTimeLiteral literal, int leftPrec, int rightPrec) {
     writer.literal(literal.toString());
diff --git a/core/src/main/java/org/apache/calcite/sql/dialect/RedshiftSqlDialect.java b/core/src/main/java/org/apache/calcite/sql/dialect/RedshiftSqlDialect.java
index 4e94977ce30..0324db47f2e 100644
--- a/core/src/main/java/org/apache/calcite/sql/dialect/RedshiftSqlDialect.java
+++ b/core/src/main/java/org/apache/calcite/sql/dialect/RedshiftSqlDialect.java
@@ -114,4 +114,8 @@ public RedshiftSqlDialect(Context context) {
   @Override public boolean supportsAliasedValues() {
     return false;
   }
+
+  @Override public boolean supportsAggregateFunctionFilter() {
+    return false;
+  }
 }
diff --git a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
index b73cc8016cf..c429c0955fd 100644
--- a/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
+++ b/core/src/test/java/org/apache/calcite/rel/rel2sql/RelToSqlConverterTest.java
@@ -314,20 +314,20 @@ private static String toSql(RelNode root, SqlDialect dialect,
         + "where \"product_id\" > 0\n"
         + "group by \"product_id\"";
     final String expectedDefault = "SELECT"
-        + " SUM(\"shelf_width\") FILTER (WHERE \"net_weight\" > 0 IS TRUE),"
+        + " SUM(\"shelf_width\") FILTER (WHERE (\"net_weight\" > 0) IS TRUE),"
         + " SUM(\"shelf_width\")\n"
         + "FROM \"foodmart\".\"product\"\n"
         + "WHERE \"product_id\" > 0\n"
         + "GROUP BY \"product_id\"";
     final String expectedBigQuery = "SELECT"
-        + " SUM(CASE WHEN net_weight > 0 IS TRUE"
+        + " SUM(CASE WHEN (net_weight > 0) IS TRUE"
         + " THEN shelf_width ELSE NULL END), "
         + "SUM(shelf_width)\n"
         + "FROM foodmart.product\n"
         + "WHERE product_id > 0\n"
         + "GROUP BY product_id";
     final String expectedFirebolt = "SELECT"
-        + " SUM(CASE WHEN \"net_weight\" > 0 IS TRUE"
+        + " SUM(CASE WHEN (\"net_weight\" > 0) IS TRUE"
         + " THEN \"shelf_width\" ELSE NULL END), "
         + "SUM(\"shelf_width\")\n"
         + "FROM \"foodmart\".\"product\"\n"
@@ -366,6 +366,33 @@ private static String toSql(RelNode root, SqlDialect dialect,
         .withBigQuery().ok(expectedBigQuery);
   }
 
+  @Test void testPivotToSqlWhenFilterIsNotSupported() {
+    String query = "select * from (\n"
+        + "  select \"brand_name\", \"net_weight\", \"product_id\"\n"
+        + "  from \"foodmart\".\"product\")\n"
+        + "  pivot (sum(\"net_weight\") as w, count(*) as c\n"
+        + "    for (\"brand_name\") in ('a', 'b'))";
+    final String expected = "SELECT \"product_id\","
+        + " SUM(\"net_weight\") FILTER (WHERE (\"brand_name\" = 'a') IS TRUE) AS \"'a'_W\","
+        + " COUNT(*) FILTER (WHERE (\"brand_name\" = 'a') IS TRUE) AS \"'a'_C\","
+        + " SUM(\"net_weight\") FILTER (WHERE (\"brand_name\" = 'b') IS TRUE) AS \"'b'_W\","
+        + " COUNT(*) FILTER (WHERE (\"brand_name\" = 'b') IS TRUE) AS \"'b'_C\"\n"
+        + "FROM \"foodmart\".\"product\"\n"
+        + "GROUP BY \"product_id\"";
+    // Redshift does not support FILTER
+    final String expectedRedshiftSql = "SELECT \"product_id\","
+        + " SUM(CASE WHEN (\"brand_name\" = 'a') IS TRUE "
+        + "THEN \"net_weight\" ELSE NULL END) AS \"'a'_W\","
+        + " COUNT(CASE WHEN (\"brand_name\" = 'a') IS TRUE THEN 1 ELSE NULL END) AS \"'a'_C\","
+        + " SUM(CASE WHEN (\"brand_name\" = 'b') IS TRUE "
+        + "THEN \"net_weight\" ELSE NULL END) AS \"'b'_W\","
+        + " COUNT(CASE WHEN (\"brand_name\" = 'b') IS TRUE THEN 1 ELSE NULL END) AS \"'b'_C\"\n"
+        + "FROM \"foodmart\".\"product\"\n"
+        + "GROUP BY \"product_id\"";
+    sql(query).ok(expected)
+        .withRedshift().ok(expectedRedshiftSql);
+  }
+
   @Test void testSimpleSelectQueryFromProductTable() {
     String query = "select \"product_id\", \"product_class_id\" from \"product\"";
     final String expected = "SELECT \"product_id\", \"product_class_id\"\n"
@@ -6282,7 +6309,7 @@ private void checkLiteral2(String expression, String expected) {
         + "within group (order by \"net_weight\" desc) filter (where \"net_weight\" > 0)"
         + "from \"product\" group by \"product_class_id\"";
     final String expected = "SELECT \"product_class_id\", COLLECT(\"net_weight\") "
-        + "FILTER (WHERE \"net_weight\" > 0 IS TRUE) "
+        + "FILTER (WHERE (\"net_weight\" > 0) IS TRUE) "
         + "WITHIN GROUP (ORDER BY \"net_weight\" DESC)\n"
         + "FROM \"foodmart\".\"product\"\n"
         + "GROUP BY \"product_class_id\"";