From 5ffac7f39fa654e815f3daf6986afd2e702a5c80 Mon Sep 17 00:00:00 2001
From: kevinyhzou <kevinyunhe8@gmail.com>
Date: Thu, 24 Oct 2024 20:02:54 +0800
Subject: [PATCH] improve performance

---
 src/Functions/UTCTimestampTransform.cpp       | 30 ++++++++++---------
 .../02812_from_to_utc_timestamp.sh            |  3 ++
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/src/Functions/UTCTimestampTransform.cpp b/src/Functions/UTCTimestampTransform.cpp
index 619951b8113..41f7f5fe749 100644
--- a/src/Functions/UTCTimestampTransform.cpp
+++ b/src/Functions/UTCTimestampTransform.cpp
@@ -27,7 +27,7 @@ namespace ErrorCodes
 
 namespace
 {
-    template <typename Name>
+    template <typename Name, bool to>
     class UTCTimestampTransform : public IFunction
     {
     public:
@@ -77,7 +77,7 @@ namespace
             if (!time_zone_const_col)
                 throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of 2nd argument of function {}. Excepted const(String).", arg2.column->getName(), name);
             String time_zone_val = time_zone_const_col->getDataAt(0).toString();
-            const DateLUTImpl & utc_time_zone = DateLUT::instance("UTC");
+            const DateLUTImpl & time_zone = DateLUT::instance(time_zone_val);
             if (WhichDataType(arg1.type).isDateTime())
             {
                 const auto & date_time_col = checkAndGetColumn<ColumnDateTime>(*arg1.column);
@@ -87,13 +87,15 @@ namespace
                 for (size_t i = 0; i < input_rows_count; ++i)
                 {
                     UInt32 date_time_val = date_time_col.getElement(i);
-                    LocalDateTime date_time(date_time_val, Name::to ? utc_time_zone : DateLUT::instance(time_zone_val));
-                    time_t time_val = date_time.to_time_t(Name::from ? utc_time_zone : DateLUT::instance(time_zone_val));
-                    result_data[i] = static_cast<UInt32>(time_val);
+                    auto timezoneOffset = time_zone.timezoneOffset(date_time_val);
+                    if constexpr (to)
+                        result_data[i] = date_time_val - static_cast<UInt32>(timezoneOffset);
+                    else
+                        result_data[i] = date_time_val + static_cast<UInt32>(timezoneOffset);
                 }
                 return result_column;
             }
-            if (WhichDataType(arg1.type).isDateTime64())
+            else if (WhichDataType(arg1.type).isDateTime64())
             {
                 const auto & date_time_col = checkAndGetColumn<ColumnDateTime64>(*arg1.column);
                 const DataTypeDateTime64 * date_time_type = static_cast<const DataTypeDateTime64 *>(arg1.type.get());
@@ -107,8 +109,12 @@ namespace
                     DateTime64 date_time_val = date_time_col.getElement(i);
                     Int64 seconds = date_time_val.value / scale_multiplier;
                     Int64 micros = date_time_val.value % scale_multiplier;
-                    LocalDateTime date_time(seconds, Name::to ? utc_time_zone : DateLUT::instance(time_zone_val));
-                    time_t time_val = date_time.to_time_t(Name::from ? utc_time_zone : DateLUT::instance(time_zone_val));
+                    auto timezoneOffset = time_zone.timezoneOffset(seconds);
+                    Int64 time_val = seconds;
+                    if constexpr (to)
+                        time_val -= timezoneOffset;
+                    else
+                        time_val += timezoneOffset;
                     DateTime64 date_time_64(time_val * scale_multiplier + micros);
                     result_data[i] = date_time_64;
                 }
@@ -122,19 +128,15 @@ namespace
     struct NameToUTCTimestamp
     {
         static constexpr auto name = "toUTCTimestamp";
-        static constexpr auto from = false;
-        static constexpr auto to = true;
     };
 
     struct NameFromUTCTimestamp
     {
         static constexpr auto name = "fromUTCTimestamp";
-        static constexpr auto from = true;
-        static constexpr auto to = false;
     };
 
-    using ToUTCTimestampFunction = UTCTimestampTransform<NameToUTCTimestamp>;
-    using FromUTCTimestampFunction = UTCTimestampTransform<NameFromUTCTimestamp>;
+    using ToUTCTimestampFunction = UTCTimestampTransform<NameToUTCTimestamp, true>;
+    using FromUTCTimestampFunction = UTCTimestampTransform<NameFromUTCTimestamp, false>;
 }
 
 REGISTER_FUNCTION(UTCTimestampTransform)
diff --git a/tests/queries/0_stateless/02812_from_to_utc_timestamp.sh b/tests/queries/0_stateless/02812_from_to_utc_timestamp.sh
index 59a6399ee2f..835dab8af57 100755
--- a/tests/queries/0_stateless/02812_from_to_utc_timestamp.sh
+++ b/tests/queries/0_stateless/02812_from_to_utc_timestamp.sh
@@ -12,4 +12,7 @@ ${CLICKHOUSE_CLIENT} -q "INSERT INTO test_tbl values(1, '2023-03-16', '2023-03-1
 ${CLICKHOUSE_CLIENT} -q "INSERT INTO test_tbl values(2, '2023-03-16 11:22:33', '2023-03-16')"
 ${CLICKHOUSE_CLIENT} -q "INSERT INTO test_tbl values(3, '2023-03-16 11:22:33', '2023-03-16 11:22:33.123456')"
 $CLICKHOUSE_CLIENT -q "select x, to_utc_timestamp(toDateTime('2023-03-16 11:22:33'), 'Etc/GMT+1'), from_utc_timestamp(toDateTime64('2023-03-16 11:22:33', 3), 'Etc/GMT+1'), to_utc_timestamp(y, 'Asia/Shanghai'), from_utc_timestamp(z, 'Asia/Shanghai') from test_tbl order by x"
+# timestamp convert between DST timezone and UTC
+$CLICKHOUSE_CLIENT -q "select to_utc_timestamp(toDateTime('2024-02-24 11:22:33'), 'Europe/Madrid'), from_utc_timestamp(toDateTime('2024-02-24 11:22:33'), 'Europe/Madrid')"
+$CLICKHOUSE_CLIENT -q "select to_utc_timestamp(toDateTime('2024-10-24 11:22:33'), 'Europe/Madrid'), from_utc_timestamp(toDateTime('2024-10-24 11:22:33'), 'Europe/Madrid')"
 $CLICKHOUSE_CLIENT -q "drop table test_tbl"
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