DB-MYSQL查询帮助选择在哪里

Question

我创建了一个名为suburb_temperature的表，它基本上保存了郊区名称，日期和温度，如下所示。

CREATE TABLE `test`.`suburb_temperature` (
  `idsuburb_temperature` INT NOT NULL AUTO_INCREMENT,
  `suburb_name` VARCHAR(100) NOT NULL,
  `time_value` DATETIME NOT NULL,
  `degrees` DOUBLE NOT NULL,
  PRIMARY KEY (`idsuburb_temperature`),
  INDEX `suburb_temperature_idx1` (`suburb_name` ASC, `time_value` ASC, `degrees` ASC));

然后我将一些数据插入此表。

INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('SYDNEY', '2015-06-16', '11.5');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('SYDNEY', '2015-06-17', '12.5');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('ULTIMO', '2015-06-16', '11');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('ULTIMO', '2015-06-17', '11.9');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('PYRMONT', '2015-06-16', '12.4');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('PYRMONT', '2015-06-17', '12.8');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('RIVERWOOD', '2015-06-16', '13.1');
INSERT INTO `test`.`suburb_temperature` (`suburb_name`, `time_value`, `degrees`) VALUES ('RIVERWOOD', '2015-06-17', '12.7');

我想找到的是郊区的平均温度，最低温度和最高温度。

我已经创建了下面运行的查询，但问题是没有为表中不存在的郊区返回任何结果。 E.G在下面的查询中，我输入了HAYMARKET作为不存在的郊区名称。使用HAYMARKET的郊区名称不会返回任何结果。我需要在返回结果中看到HAYMARKET的最小值，最大值和平均值为0。有谁知道如何有效地实现这一目标？

SELECT suburb_name,
IFNULL(ROUND(avg(suburb_temperature.degrees),2),0) as 'SUBURB_AVG_TEMP_DEGREES_CELCIUS',
IFNULL(ROUND(min(suburb_temperature.degrees),2),0) as 'SUBURB_MIN_TEMP_DEGREES_CELCIUS',
IFNULL(ROUND(max(suburb_temperature.degrees),2),0) as 'SUBURB_MAX_TEMP_DEGREES_CELCIUS'
FROM suburb_temperature
WHERE suburb_name IN('HAYMARET','PYRMONT','RIVERWOOD','SYDNEY','ULTIMO')
GROUP BY suburb_name
ORDER BY suburb_name asc

以上查询的结果如下：

Answer 1

我根据您的要求修改了SQL。

 SELECT b.suburb_name,
IFNULL(ROUND(AVG(a.degrees),2),0) AS 'SUBURB_AVG_TEMP_DEGREES_CELCIUS',
IFNULL(ROUND(MIN(a.degrees),2),0) AS 'SUBURB_MIN_TEMP_DEGREES_CELCIUS',
IFNULL(ROUND(MAX(a.degrees),2),0) AS 'SUBURB_MAX_TEMP_DEGREES_CELCIUS'
FROM suburb_temperature AS a RIGHT JOIN  (SELECT 'HAYMARET' AS 'suburb_name' UNION SELECT 'PYRMONT' AS 'suburb_name' UNION SELECT 'RIVERWOOD' AS 'suburb_name' 
UNION SELECT 'SYDNEY' AS 'suburb_name' UNION SELECT 'ULTIMO' AS 'suburb_name') AS b 
ON a.suburb_name = b.suburb_name
GROUP BY suburb_name
ORDER BY suburb_name ASC

我认为你的问题会解决。

谢谢。