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From: Frank-Gu-81 (@Frank-Gu-81) <[email protected]>
To: pgjdbc/pgjdbc <[email protected]>
Subject: Re: [pgjdbc/pgjdbc] issue #3692: Wrong time formatting ResultSet.getTime(); for Europe/Belgrade and "Europe/Prague"
Date: Thu, 21 Aug 2025 22:06:38 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Thanks for the discussion — following up with another observation that might help narrow this down. 

## Context

I’m also seeing a possible time-of-day mismatch around DST when calling `ResultSet#getTime(int)` without a Calendar on `TIMESTAMP` / `TIMESTAMPTZ`.


## Environment

* PgJDBC: 42.7.7
* Java: 21
* PostgreSQL server: 16.4
* OS: macOS 15.6
* JVM default timezone at runtime: America/Los_Angeles 

## Steps to reproduce

1. Set the JVM default zone to America/Los_Angeles (any DST-observing zone should work):

   ```java
   TimeZone.setDefault(TimeZone.getTimeZone("America/Los_Angeles"));


2. Create a table and insert two rows (one in standard time, one in DST):

  ```sql
  CREATE TEMP TABLE test_timestamps (
    ts_without_tz timestamp,
    ts_with_tz    timestamptz
  );
  
 INSERT INTO test_timestamps VALUES
  ('2023-11-10 09:00:00', '2023-11-10 09:00:00-08'), -- PST (UTC-8)
  ('2023-03-13 09:00:00', '2023-03-13 09:00:00-07'); -- PDT (UTC-7)
  ```

3. Query and call `rs.getTime(col)` (no Calendar) on each column. 

```java
try (var c = DriverManager.getConnection(PG_URL);
     var s = c.createStatement();
     var rs = s.executeQuery("select ts_without_tz, ts_with_tz from test_timestamps order by 1")) {

  while (rs.next()) {
    var tNoCal_noTz = rs.getTime(1);         // no Calendar
    var tNoCal_tz   = rs.getTime(2);         // no Calendar

    var ts          = rs.getTimestamp(2);    // compare against local wall-clock at the instant
    var lt          = ts.toInstant().atZone(ZoneId.systemDefault()).toLocalTime();

    System.out.printf("noCal timestamp=%s getTime=%s localTimeAtInstant=%s%n", ts, tNoCal_tz, lt);
  }
}
```

## Observed vs expected (America/Los_Angeles)

* 2023-11-10  09:00 → `getTime(...)` returns 09:00:00 (as expected).
* 2023-03-13 09:00 → `getTime(...)` returns 08:00:00, while:

```java
var lt = ts.toInstant().atZone(ZoneId.systemDefault()).toLocalTime(); // → 09:00
```

shows 09:00 at that instant in the JVM zone.


## Possible cause

This seems consistent with the 1970-01-01 “epoch rebasing” noted earlier, and I think it's coming from the `PgResultSet#getTime(..)` path ending up in `TimestampUtils.convertToTime(...)`. Per its docs, `convertToTime()` normalizes the value so the date part becomes 1970-01-01 in the selected timezone. 

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  Subject: Re: [pgjdbc/pgjdbc] issue #3692: Wrong time formatting ResultSet.getTime(); for Europe/Belgrade and "Europe/Prague"
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