SQL TZ Convert

SqlTimeZoneConvert.cs

using System.Data.SqlClient;

internal class Program
{
    static void Main(string[] args)
    {
        var dbStr = args[0];
        var srcTz = args[1];
        var dstTz = args[2];

        string srv, db;
        if (dbStr.Contains(':'))
        {
            srv = dbStr.Substring(0, dbStr.IndexOf(':'));
            db = dbStr.Substring(dbStr.IndexOf(':')+1);
        }
        else
        {
            srv = ".";
            db = dbStr;
        }

        var csb = new SqlConnectionStringBuilder()
        {
            DataSource = srv,
            InitialCatalog = db,
            IntegratedSecurity = true,
            TrustServerCertificate = true,
        };

        var conn = new SqlConnection(csb.ConnectionString);
        conn.Open();
        DatabaseTimeZoneUpdate.UpdateTimeZone(conn, srcTz, dstTz);
    }
}

// a process to update all datetime values to be in a given timezone
public static class DatabaseTimeZoneUpdate
{
    public static void ValidateTimeZone(SqlConnection conn, string tzId)
    {
        using var cmd = conn.CreateCommand();
        cmd.CommandText = "select count(1) from sys.time_zone_info where name = @id";
        cmd.Parameters.AddWithValue("id", tzId);
        if (cmd.ExecuteScalar() is not 1)
        {
            throw new ArgumentOutOfRangeException(nameof(tzId), $"Timezone {tzId} is not known by SqlServer");
        }
    }

    public static void UpdateTimeZone(SqlConnection conn, string srcTzId, string dstTzId)
    {
        // Validate that the timezone names are correct.
        ValidateTimeZone(conn, srcTzId);
        ValidateTimeZone(conn, dstTzId);

        var cmd = conn.CreateCommand();

        // get all the datetime and datetime2 columns in the database.
        cmd.CommandText =
            """
            select
                  s.name as schemaName,
                  ta.name as tableName,
                  c.name as columnName,
                  t.name as typeName
            from sys.columns c
            join sys.tables ta
                  on c.object_id = ta.object_id
            join sys.schemas s
                  on ta.schema_id = s.schema_id

            join sys.types t
                  on c.system_type_id = t.system_type_id
            where
                  t.name in ('datetime', 'datetime2')
            order by
                  s.name, ta.name, c.name
            """;

        var sw = new StringWriter();

        using (var reader = cmd.ExecuteReader())
        {
            sw.WriteLine($"declare @SrcTzId varchar(128) = '{srcTzId}'");
            sw.WriteLine($"declare @DstTzId varchar(128) = '{dstTzId}'");

            string? table = null;

            while (reader.Read())
            {
                var schemaName = reader.GetString(0);
                var tableName = reader.GetString(1);
                var columnName = reader.GetString(2);
                var typeName = reader.GetString(3);
                if (tableName != table)
                {
                    if (table != null)
                    {
                        sw.WriteLine(";");
                    }
                    sw.WriteLine($"update [{schemaName}].[{tableName}] set ");
                    table = tableName;
                }
                else
                {
                    sw.Write(",");
                }

                sw.WriteLine($"{columnName} = {columnName} at time zone @SrcTzId at time zone @DstTzId");
            }
        }

        cmd.CommandText = sw.ToString();
        // this command can take a while.
        cmd.CommandTimeout = (int)TimeSpan.FromHours(1).TotalSeconds;
        cmd.ExecuteNonQuery();
    }
}