查看过去 x 天是否没有创建记录

Question

假设我有一个数据库来跟踪结构如下所示的浇水植物：

Table: "Plants"
ID     Plants
----------------------------------
1      Roses
2      Daisies
3      Sunflowers
4      Marigolds
5      Daffodils

Table: "Maintenance"
ID    Plant_ID    Activity    Date
-------------------------------------
1     1            Water      2011-09-09
2     1            Water      2011-08-02
3     2            Water      2011-08-15
4     3            Water      2010-07-01
5     4            Weed       2010-07-01

我正在尝试编写一个查询来告诉我们植物是否需要浇水，如果需要，浇水程度如何。换句话说：如果植物在过去 30 天内没有浇水，则返回“黄色”警告级别；如果在过去 60 天内没有浇水，则警告级别为“红色”。

这是我目前所处的位置：

SELECT Plants.Plants, 
IF ( DATEDIFF(CURRENT_DATE, MAX(Maintenance.Date)) < 30 AND maintenance.type = "Water", '',
  IF ((DATEDIFF(CURRENT_DATE, MAX(Maintenance.Date)) >= 60 AND maintenance.type = "Water") or maintenance.date IS NULL, 'Red', 'Yellow')
) AS `Water Warning`,
IF ( DATEDIFF(CURRENT_DATE, MAX(Maintenance.Date)) < 30 and maintenance.type = "Weed" , '',
  IF ((DATEDIFF(CURRENT_DATE, MAX(Maintenance.Date)) >= 60 and maintenance.type = "Weed") or maintenance.date IS NULL, 'Red', 'Yellow')
) AS `Weeding Warning`
FROM `plants`
LEFT JOIN `maintenance` ON `maintenance`.`plant_id` = `plants`.`id`
GROUP BY `plants`.`id`;

但这会为“Roses”返回“红色”警告，而不是预期的空字符串，并且没有 Maintenance.Activity 的条件。请注意，同样的查询也需要对除草和其他活动执行类似的功能，因此在 WHERE 子句中进行过滤可能不是答案。

这是我想要的：

Results
ID     Plants        "Water Warning"  "Weed Warning"
----------------------------------------------------
1      Roses               ""             "Red"
2      Daisies           "Yellow"         "Red"
3      Sunflowers         "Red"           "Red"
4      Marigolds          "Red"            ""
5      Daffodils          "Red"           "Red"

Answer 1

使用下面的语句，您只需将表格与植物名称连接起来。

SELECT *, 

CASE
    WHEN DATEDIFF(CURRENT_DATE, DATE) >= 60 THEN 'RED'
    WHEN DATEDIFF(CURRENT_DATE, DATE) >= 30 THEN 'YELLOW'
END AS FLAG
FROM test_table

Answer 2

我真的希望有一个更优雅的解决方案，但这有效：

SELECT 
`plants`.`plants`,
IF((MAX(IF(`maintenance`.`type` = 'Water',
        `maintenance`.`date`,
        NULL)) IS NULL) OR ((DATEDIFF(CURRENT_DATE,
            MAX(IF(`maintenance`.`type` = 'Water',
                `maintenance`.`date`,
                NULL)))) > 30),
    (IF((MAX(IF(`maintenance`.`type` = 'Water',
            `maintenance`.`date`,
            NULL)) IS NULL) OR ((DATEDIFF(CURRENT_DATE,
                MAX(IF(`maintenance`.`type` = 'Water',
                    `maintenance`.`date`,
                    NULL)))) > 90),
        'red',
        'yellow')),
    '') AS `Water Warning`,
IF((MAX(IF(`maintenance`.`type` = 'Weed',
        `maintenance`.`date`,
        NULL)) IS NULL) OR ((DATEDIFF(CURRENT_DATE,
            MAX(IF(`maintenance`.`type` = 'Weed',
                `maintenance`.`date`,
                NULL)))) > 30),
    (IF((MAX(IF(`maintenance`.`type` = 'Weed',
            `maintenance`.`date`,
            NULL)) IS NULL) OR ((DATEDIFF(CURRENT_DATE,
                MAX(IF(`maintenance`.`type` = 'Weed',
                    `maintenance`.`date`,
                    NULL)))) > 90),
        'red',
        'yellow')),
    '') AS `Weed Warning`
FROM
`plants`
    LEFT JOIN
`maintenance` ON `maintenance`.`plant_id` = `plants`.`id`
GROUP BY `plants`.`id`;

Answer 3

实际数据

mysql> 从植物中选择 *； +--------+------------+ |身份证 |植物 | +--------+------------+ | 1 |玫瑰 | | 2 |雏菊 | | 3 |向日葵 | | 4 |金盏花 | | 5 |水仙 | +--------+------------+ mysql> 从维护中选择 *； +----+------------+----------+------------+ |身份证 |植物_ID |活动 |日期 | +----+------------+----------+------------+ | 1 | 1 |水 | 2011-09-09 | | 2 | 1 |水 | 2011-08-02 | | 3 | 2 |水 | 2011-08-15 | | 4 | 3 |水 | 2010-07-01 | | 5 | 4 |杂草 | 2010-07-01 | +----+------------+----------+------------+

SELECT
Plants.Plants,
COALESCE(
CASE mt.Activity='Weed'
  WHEN 1 THEN
    CASE DATEDIFF(CURRENT_DATE, mt.last_date) BETWEEN 0 AND 30
      WHEN 1 THEN ''
      ELSE
        CASE DATEDIFF(CURRENT_DATE, mt.last_date) BETWEEN 30 AND 60
        WHEN 1 THEN 'Yellow'
        ELSE NULL
        END
    END
END, 'Red') AS "Weed Warning",
COALESCE(
CASE mt.Activity='Water'
  WHEN 1 THEN
    CASE DATEDIFF(CURRENT_DATE, mt.last_date) BETWEEN 0 AND 30
      WHEN 1 THEN ''
      ELSE
        CASE DATEDIFF(CURRENT_DATE, mt.last_date) BETWEEN 30 AND 60
        WHEN 1 THEN 'Yellow'
        ELSE NULL
        END
    END
END, 'Red') AS "Water Warning"
FROM Plants
LEFT JOIN
( SELECT Plant_ID, Activity, MAX(Date) AS last_date
  FROM Maintenance
  GROUP BY Plant_ID, Activity) AS mt ON Plants.ID=mt.Plant_ID
GROUP BY Plants.ID;

结果

+------------+--------------+----------------+ |植物 |杂草警告 |水警告 | +------------+--------------+----------------+ |玫瑰 |红色 | | |雏菊 |红色 | | |向日葵 |红色 |红色 | |金盏花 |红色 |红色 | |水仙 |红色 |红色 | +------------+--------------+----------------+

OP 说明

1. 您发布了错误的结果
2. 您已参考不存在列type
3. 您没有注意表名是否区分大小写