[Coral-Trino] Modify transformation for CURRENT_TIMESTAMP

coral-trino/src/main/java/com/linkedin/coral/trino/rel2trino/transformers/CurrentTimestampTransformer.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2023 LinkedIn Corporation. All rights reserved.
+ * Copyright 2023-2024 LinkedIn Corporation. All rights reserved.
  * Licensed under the BSD-2 Clause license.
  * See LICENSE in the project root for license information.
  */
@@ -8,6 +8,10 @@
 import org.apache.calcite.sql.SqlBasicTypeNameSpec;
 import org.apache.calcite.sql.SqlCall;
 import org.apache.calcite.sql.SqlDataTypeSpec;
+import org.apache.calcite.sql.SqlFunction;
+import org.apache.calcite.sql.SqlFunctionCategory;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.SqlSyntax;
 import org.apache.calcite.sql.fun.SqlStdOperatorTable;
 import org.apache.calcite.sql.parser.SqlParserPos;
 import org.apache.calcite.sql.type.SqlTypeName;
@@ -17,12 +21,16 @@
 
 /**
  * This class implements the transformation for the CURRENT_TIMESTAMP function.
- * For example, "SELECT CURRENT_TIMESTAMP" is transformed into "SELECT CAST(CURRENT_TIMESTAMP AS TIMESTAMP(3))".
- * This transformation ensures compatibility with Trino.
+ * For example, "SELECT CURRENT_TIMESTAMP" is transformed into "SELECT CAST(CURRENT_TIMESTAMP AT TIME ZONE 'UTC' AS TIMESTAMP(3))".
+ * This transformation ensures compatibility with Trino due to the following reasons:
+ * (1) In Hive, CURRENT_TIMESTAMP returns a UTC timestamp, whereas in Trino, it returns a timestamp based on the session's timezone.
+ * (2) In Hive, the return type of CURRENT_TIMESTAMP is timestamp, whereas in Trino, the return type is timestamp with time zone,
+ * so we need to add an explicit CAST.
  */
 public class CurrentTimestampTransformer extends SqlCallTransformer {
 
   private static final String CURRENT_TIMESTAMP_FUNCTION_NAME = "CURRENT_TIMESTAMP";
+  private static final String CURRENT_TIMESTAMP_AT_TIMEZONE_UTC = "CURRENT_TIMESTAMP AT TIME ZONE 'UTC'";
 
   @Override
   protected boolean condition(SqlCall sqlCall) {
@@ -33,6 +41,17 @@ protected boolean condition(SqlCall sqlCall) {
   protected SqlCall transform(SqlCall sqlCall) {
     SqlDataTypeSpec timestampType =
         new SqlDataTypeSpec(new SqlBasicTypeNameSpec(SqlTypeName.TIMESTAMP, 3, SqlParserPos.ZERO), SqlParserPos.ZERO);
-    return SqlStdOperatorTable.CAST.createCall(SqlParserPos.ZERO, sqlCall, timestampType);
+    final SqlOperator currentTimestampOperator = sqlCall.getOperator();
+    final SqlFunction currentTimestampAtTimeZoneUTCOperator =
+        new SqlFunction(CURRENT_TIMESTAMP_AT_TIMEZONE_UTC, currentTimestampOperator.kind,
+            currentTimestampOperator.getReturnTypeInference(), currentTimestampOperator.getOperandTypeInference(),
+            currentTimestampOperator.getOperandTypeChecker(), SqlFunctionCategory.TIMEDATE) {
+          @Override
+          public SqlSyntax getSyntax() {
+            return SqlSyntax.FUNCTION_ID;
+          }
+        };
+    return SqlStdOperatorTable.CAST.createCall(SqlParserPos.ZERO,
+        currentTimestampAtTimeZoneUTCOperator.createCall(SqlParserPos.ZERO, sqlCall.getOperandList()), timestampType);
   }
 }

coral-trino/src/test/java/com/linkedin/coral/trino/rel2trino/HiveToTrinoConverterTest.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2017-2023 LinkedIn Corporation. All rights reserved.
+ * Copyright 2017-2024 LinkedIn Corporation. All rights reserved.
  * Licensed under the BSD-2 Clause license.
  * See LICENSE in the project root for license information.
  */
@@ -136,7 +136,7 @@ public Object[][] viewTestCasesProvider() {
         { "test", "map_array_view", "SELECT MAP (ARRAY['key1', 'key2'], ARRAY['value1', 'value2']) AS \"simple_map_col\", MAP (ARRAY['key1', 'key2'], ARRAY[MAP (ARRAY['a', 'c'], ARRAY['b', 'd']), MAP (ARRAY['a', 'c'], ARRAY['b', 'd'])]) AS \"nested_map_col\"\n"
             + "FROM \"test\".\"tablea\" AS \"tablea\"" },
 
-        { "test", "current_date_and_timestamp_view", "SELECT CAST(CURRENT_TIMESTAMP AS TIMESTAMP(3)), TRIM(CAST(CAST(CURRENT_TIMESTAMP AS TIMESTAMP(3)) AS VARCHAR(65535))) AS \"ct\", CURRENT_DATE, CURRENT_DATE AS \"cd\", \"tablea\".\"a\" AS \"a\"\n"
+        { "test", "current_date_and_timestamp_view", "SELECT CAST(CURRENT_TIMESTAMP AT TIME ZONE 'UTC' AS TIMESTAMP(3)), TRIM(CAST(CAST(CURRENT_TIMESTAMP AT TIME ZONE 'UTC' AS TIMESTAMP(3)) AS VARCHAR(65535))) AS \"ct\", CURRENT_DATE, CURRENT_DATE AS \"cd\", \"tablea\".\"a\" AS \"a\"\n"
             + "FROM \"test\".\"tablea\" AS \"tablea\"" },
 
         { "test", "date_function_view", "SELECT \"date\"('2021-01-02') AS \"a\"\n"

coral-trino/src/test/java/com/linkedin/coral/trino/rel2trino/RelToTrinoConverterTest.java

@@ -1,5 +1,5 @@
 /**
- * Copyright 2017-2023 LinkedIn Corporation. All rights reserved.
+ * Copyright 2017-2024 LinkedIn Corporation. All rights reserved.
  * Licensed under the BSD-2 Clause license.
  * See LICENSE in the project root for license information.
  */
@@ -510,8 +510,8 @@ public void testCurrentUser() {
   @Test
   public void testCurrentTimestamp() {
     String sql = "SELECT current_timestamp";
-    String expected =
-        formatSql("SELECT CAST(CURRENT_TIMESTAMP AS TIMESTAMP(3))\nFROM (VALUES  (0)) AS \"t\" (\"ZERO\")");
+    String expected = formatSql(
+        "SELECT CAST(CURRENT_TIMESTAMP AT TIME ZONE 'UTC' AS TIMESTAMP(3))\nFROM (VALUES  (0)) AS \"t\" (\"ZERO\")");
     testConversion(sql, expected);
   }