[jdbc] Incorrect DateTime results when writing numeric data with use_time_zone property

[haishui126]

Describe the bug

The DateTime results will -8h when inserting long values using PrepareStatement with use_server_time_zone=false&use_time_zone=Asia/Shanghai. (ClickHouse Server timezone is UTC)

Expected: '1970-01-01 08:00:00.001000000'
Actual: '1970-01-01 00:00:00.001000000'
(timezone is Asia/Shanghai)

Code example

CREATE TABLE t_test
(
    `timestamp` DateTime64(3)
)
ENGINE = Log;

try (
    Connection connection = DriverManager.getConnection("jdbc:ch://localhost:8123/default?use_server_time_zone=false&use_time_zone=Asia/Shanghai", "default", "");
    PreparedStatement preparedStatement = connection.prepareStatement("INSERT INTO t_test VALUES (?)")
) {
    preparedStatement.setLong(1, 1);
    preparedStatement.execute();
}

Configuration

Environment

• Client version: 0.7.2
• Language version: java11

[haishui126]

Hi team,
I think the method in com.clickhouse.data.ClickHouseValues.java:282 is incorrect. Why should a numeric type representing a Unix timestamp, which inherently lacks timezone context, be directly converted to a LocalDateTime assuming it's in the UTC time zone?

public static LocalDateTime convertToDateTime(BigDecimal value) {
    return value != null ? LocalDateTime.ofInstant(convertToInstant(value), ZoneOffset.UTC) : null;
}

The concern here is that the conversion assumes the input Unix timestamp is in UTC without verifying if this is correct for all cases, which can lead to time zone discrepancies when clients operate in different time zones.