根据用户输入在 PreparedStatement 中使用 setTime() 或 setNull()

Question

我正在我的 JAVA 应用程序和 PostgreSQL 数据库中进行过滤搜索。

我有以下用于选择航班数据的 PostgreSQL 查询：

String query =  "SELECT flight.flight_id, route.from_location, route.to_location, flight.base_cost, flight.departure_date, flight.departure_time, flight.arrival_date, flight.arrival_time, aircraft.manufacturer, aircraft.seats " +
                "FROM flight " +
                "INNER JOIN route ON flight.route_id = route.route_id " +
                "INNER JOIN aircraft ON flight.aircraft_id = aircraft.aircraft_id " +
                "WHERE " +
                "(from_location = CASE WHEN ? IS NULL THEN from_location ELSE ? END) AND " +
                "(to_location = CASE WHEN ? IS NULL THEN to_location ELSE ? END) AND " +
                "(base_cost = CASE WHEN ? IS NULL THEN base_cost ELSE ? END) AND " +
                "(departure_date = CASE WHEN ? IS NULL THEN departure_date ELSE ? END) AND " +
                "(departure_time = CASE WHEN ? IS NULL THEN departure_time ELSE ? END) AND " +
                "(arrival_date = CASE WHEN ? IS NULL THEN arrival_date ELSE ? END) AND " +
                "(arrival_time = CASE WHEN ? IS NULL THEN arrival_time ELSE ? END)";

然后我有一个这样的Java代码：

    ResultSet rs = null;
    PreparedStatement prepStatement = connection.prepareStatement(query);
    try {
                if (!showFromTxtField.getText().trim().isEmpty()) {
                    prepStatement.setString(1, showFromTxtField.getText());
                    prepStatement.setString(2, showFromTxtField.getText());
                } else {
                    prepStatement.setNull(1, java.sql.Types.VARCHAR );
                    prepStatement.setNull(2, java.sql.Types.VARCHAR );
                }
                if (!showToTxtField.getText().trim().isEmpty()) {
                    prepStatement.setString(3, showToTxtField.getText());
                    prepStatement.setString(4, showToTxtField.getText());
                } else {
                    prepStatement.setNull(3, java.sql.Types.VARCHAR );
                    prepStatement.setNull(4, java.sql.Types.VARCHAR );
                }
                if (!showCostTxtField.getText().trim().isEmpty()) {
                    prepStatement.setFloat(5, Float.parseFloat(showCostTxtField.getText()));
                    prepStatement.setFloat(6, Float.parseFloat(showCostTxtField.getText()));
                } else {
                    prepStatement.setNull(5, java.sql.Types.FLOAT );
                    prepStatement.setNull(6, java.sql.Types.FLOAT);
                }
                LocalDate depDate = showDepDateDatePicker.getValue();
                if (depDate != null) {
                    prepStatement.setDate(7, Date.valueOf(depDate));
                    prepStatement.setDate(8, Date.valueOf(depDate));
                } else {
                    prepStatement.setNull(7, java.sql.Types.DATE );
                    prepStatement.setNull(8, java.sql.Types.DATE);
                }
                if (!showDepTimeTxtField.getText().trim().isEmpty()) {
                    DateFormat formatter = new SimpleDateFormat("HH:mm:ss");
                    try {
                        Time timeValue = new Time(formatter.parse(showDepTimeTxtField.getText()).getTime());
                        prepStatement.setTime(9, timeValue);
                        prepStatement.setTime(10, timeValue);
                    } catch (ParseException e) {
                        e.printStackTrace();
                    }
                } else {
                    prepStatement.setNull(9, java.sql.Types.TIME );
                    prepStatement.setNull(10, java.sql.Types.TIME );
                }
                LocalDate arrDate = showArrDatePicker.getValue();
                if (arrDate != null) {
                    prepStatement.setDate(11, Date.valueOf(arrDate));
                    prepStatement.setDate(12, Date.valueOf(arrDate));
                } else {
                    prepStatement.setNull(11, java.sql.Types.DATE );
                    prepStatement.setNull(12, java.sql.Types.DATE);
                }
                if (!showArrTimeTxtField.getText().trim().isEmpty()) {
                    DateFormat formatter = new SimpleDateFormat("HH:mm:ss");
                    try {
                        Time timeValue = new Time(formatter.parse(showArrTimeTxtField.getText()).getTime());
                        prepStatement.setTime(13, timeValue);
                        prepStatement.setTime(14, timeValue);
                    } catch (ParseException e) {
                        e.printStackTrace();
                    }
                } else {
                    prepStatement.setNull(13, java.sql.Types.TIME );
                    prepStatement.setNull(14, java.sql.Types.TIME );
                }

                rs = prepStatement.executeQuery();
      } catch (SQLException e) {
                e.printStackTrace();
            }

因此，重点是仅返回符合文本字段条件的航班。如果任何文本字段留空，则查询应返回符合该特定条件的所有航班，但会使用其他非空条件进行过滤。

我在参数 $9 处出错。 当我将输入showDepTimeTxtField 的String（例如“18:00:00”）转换为java.sql.Time 对象时，我可以将其用作prepStatement 方法setTime() 的输入参数，我的查询应该只返回航班（已满足其他标准）departure_time 与在文本字段中输入的时间相同。如果文本字段为空且没有 String 输入，我的查询应该从我的数据库中返回带有 departure_time 的航班。

我的问题是，当我运行我的代码时，出现以下错误： org.postgresql.util.PSQLException: ERROR: could not determine data type of parameter $9 无论我用字符串填充departureTimeTxtField 还是将其留空，所以参数departure_time 应该设置为NULL 并且我的查询应该返回所有 departure_time 的航班。

所以我假设我对 setTime() 方法参数 timeValue 以及从 String 到 java.sql.Time 的转换有问题。

如何进行正确的转换以消除该错误？

编辑：SQL 查询和 Java 源代码已更新。

Answer 1

我能够通过使用COALESCE() 而不是CASE WHEN ... 来解决这个问题：

String query = "SELECT * FROM flights WHERE departure_time = COALESCE(?, departure_time)";

Answer 2

该错误是由于 SQL 中无效的CASE 语法（而不是因为时间格式）而产生的，请查看CASE 语法here。

此外，从示例中，您似乎正在尝试获取起飞时间为空或文本字段中存在时间的所有航班，在这种情况下，我建议采用以下方法：

ResultSet rs = null;
PreparedStatement prepStatement = null;
if (!departureTimeTxtField.getText().trim().isEmpty()) {
    DateFormat formatter = new SimpleDateFormat("HH:mm:ss");
    Time timeValue = new Time(formatter.parse(departureTimeTxtField.getText()).getTime());
    prepStatement  = connection.prepareStatement("SELECT * FROM flights WHERE departure_time = ?");
    prepStatement.setTime(1, timeValue);
}else{
    prepStatement  = connection.prepareStatement("SELECT * FROM flights WHERE departure_time IS NULL");
}
rs = prepStatement.executeQuery();