用于设置列值不起作用的SQL CASE语句

时间：2017-10-27 02:08:10

标签： sql postgresql

我有一个连接几个表的查询，我试图使用case语句创建几个列来确定不能按预期工作的值（超链接文本）。我想查看连接产生的行，如果其中一个左连接的值不为null，那么我想将一些文本与值连接起来，如果它是null，我将用不同的值连接文本。查询是：

SELECT p.*, p.id AS ppe_id, CONCAT(u.last_name, ',', u.first_name) 
    AS name, sub1.created_at AS last_inspection,
  CASE
    WHEN (sub1.created_at IS NULL AND man_date < now() - interval '1 year'  )
    THEN 'over-due'
    WHEN (sub1.created_at IS NULL AND man_date < now() - interval '11 months'  )
    THEN 'due'
    WHEN sub1.created_at < now() - interval '11 months'
    THEN 'due'
    WHEN sub1.created_at < now() - interval '1 year'
    THEN 'over-due'
    ELSE 'none'
  END
    AS inspection_due, 
  CASE 
    WHEN now() > p.man_date + interval '10 years' 
    THEN 'over-due' 
    WHEN now() > p.man_date + interval '119 months' 
    THEN 'due' 
    ELSE 'none' 
  END 
  AS expiring,
  CASE 
    WHEN cl_sub.ppe_id IS NOT NULL
    THEN '<a class="btn btn-xs btn-back" href="/cleanings/' || cl_sub.id || '">Cleaning</a>'
    WHEN cl_sub.ppe_id IS NULL
    THEN '<a class="btn btn-xs btn-success" href="/ppes/'|| cl_sub.ppe_id || '/cleanings/new">Clean</a>'
  END
  AS cleaning_button,
  CASE
    WHEN r_sub.ppe_id IS NOT NULL
    THEN '<a class="btn btn-xs btn-back" href="/repairs/' || r_sub.id || '">Repairing</a>'
    WHEN r_sub.ppe_id IS NULL
    THEN'<a class="btn btn-xs btn-success" href="/ppes/' || r_sub.ppe_id || '/repairs/new">Repair</a>'
  END
  AS repair_button     
FROM  ppes p
  JOIN users u
  ON p.user_id = u.id 
  LEFT OUTER JOIN (SELECT DISTINCT ppe_id, id FROM cleanings cl WHERE cleaning_date IS NULL ) AS cl_sub 
  ON p.id = cl_sub.ppe_id
  LEFT OUTER JOIN (SELECT DISTINCT ppe_id, id FROM repairs r WHERE completed IS NULL ) AS r_sub
  ON p.id = r_sub.ppe_id 
LEFT OUTER JOIN (SELECT t.ppe_id, t.created_at
      FROM inspections t
    INNER JOIN (SELECT ppe_id, max(created_at) as LastInsp
          FROM inspections
          GROUP BY ppe_id ) tm
          ON t.ppe_id = tm.ppe_id AND t.created_at = tm.LastInsp
      WHERE (t.advanced = true AND t.passed = true) order by t.ppe_id) AS sub1
ON sub1.ppe_id = p.id;

问题在于，即使两个连接产生了预期的效果，即它们要么为子查询中的任何一个提出id，要么得出null，我只从每个case语句的前半部分得到输出：

CASE 
WHEN cl_sub.ppe_id IS NOT NULL
THEN '<a class="btn btn-xs btn-back" href="/cleanings/' || cl_sub.id || '">Cleaning</a>'
WHEN cl_sub.ppe_id IS NULL
THEN '<a class="btn btn-xs btn-success" href="/ppes/'|| cl_sub.ppe_id || '/cleanings/new">Clean</a>'
END
AS cleaning_button,
CASE
WHEN r_sub.ppe_id IS NOT NULL
THEN '<a class="btn btn-xs btn-back" href="/repairs/' || r_sub.id || '">Repairing</a>'
WHEN r_sub.ppe_id IS NULL
THEN'<a class="btn btn-xs btn-success" href="/ppes/' || r_sub.ppe_id || '/repairs/new">Repair</a>'
END
AS repair_button

如果我在表中查询这些字段，它会显示清理表或修复表在连接中返回ID的情况，它会输入所需的值，但是否则会将其留空而不是放入第二个案例陈述中的价值：

ppe_development=# select id, cleaning_button, repair_button from test_view_ppes  order by cleaning_button, repair_button;
 id  |                         cleaning_button                          |                          repair_button                          
-----+------------------------------------------------------------------+-----------------------------------------------------------------
 126 | <a class="btn btn-xs btn-back" href="/cleanings/13">Cleaning</a> | 
  13 | <a class="btn btn-xs btn-back" href="/cleanings/24">Cleaning</a> | 
 115 | <a class="btn btn-xs btn-back" href="/cleanings/27">Cleaning</a> | 
 113 | <a class="btn btn-xs btn-back" href="/cleanings/5">Cleaning</a>  | <a class="btn btn-xs btn-back" href="/repairs/3">Repairing</a>
 114 | <a class="btn btn-xs btn-back" href="/cleanings/6">Cleaning</a>  | <a class="btn btn-xs btn-back" href="/repairs/14">Repairing</a>
  53 | <a class="btn btn-xs btn-back" href="/cleanings/8">Cleaning</a>  | 
   1 | <a class="btn btn-xs btn-back" href="/cleanings/9">Cleaning</a>  | <a class="btn btn-xs btn-back" href="/repairs/13">Repairing</a>
  54 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/16">Repairing</a>
  57 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/17">Repairing</a>
  56 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/22">Repairing</a>
  58 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/25">Repairing</a>
 118 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/26">Repairing</a>
   7 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/28">Repairing</a>
  15 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/30">Repairing</a>
  11 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/32">Repairing</a>
 120 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/33">Repairing</a>
 123 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/5">Repairing</a>
 116 |                                                                  | <a class="btn btn-xs btn-back" href="/repairs/7">Repairing</a>
  78 |                                                                  |

ppes table：

id | serial |  man_date  | category |         created_at         |         updated_at         | user_id | note | size | manufacturer | active | cost | cbrn_rated 
---+--------+------------+----------+----------------------------+----------------------------+---------+------+------+--------------+--------+------+------------
12 | 10007  | 2017-01-25 | jackets  | 2017-01-25 17:40:10.652715 | 2017-04-11 00:46:58.154629 |       5 |      |      |              | t      | 0.00 | 
18 | 10013  | 2017-01-25 | jackets  | 2017-01-25 17:40:10.663324 | 2017-04-11 00:46:58.187638 |       6 |      |      |              | t      | 0.00 | 
20 | 10015  | 2017-01-25 | gloves   | 2017-01-25 17:40:10.66659  | 2017-04-11 00:46:58.199712 |       6 |      |      |              | t      | 0.00 | 
24 | 10019  | 2017-01-25 | jackets  | 2017-01-25 17:40:10.673236 | 2017-04-11 00:46:58.228069 |       8 |      |      |              | t      | 0.00 | 
26 | 10021  | 2017-01-25 | gloves   | 2017-01-25 17:40:10.67665  | 2017-04-11 00:46:58.239997 |       8 |      |      |              | t      | 0.00 |

清洁表：

id | cleaning_date | user_id | ppe_id |           notes            |         created_at         |         updated_at         | failed_inspection 
---+---------------+---------+--------+----------------------------+----------------------------+----------------------------+-------------------
 5 |               |       1 |    113 | 1                          | 2017-04-01 21:11:28.882502 | 2017-04-01 21:11:28.882502 | f
 6 |               |       1 |    114 | 2                          | 2017-04-01 21:11:41.068899 | 2017-04-01 21:11:41.068899 | f
 8 |               |       1 |     53 | Bamboo                     | 2017-04-07 19:36:17.48159  | 2017-04-07 19:36:17.48159  | f
13 |               |       1 |    126 | testing new routing        | 2017-06-25 20:38:16.813986 | 2017-06-25 20:38:16.813986 | f

维修表：

id | order_date | completed | user_id | ppe_id |        notes         |         created_at         |         updated_at         | failed_inspection | cost 
---+------------+-----------+---------+--------+----------------------+----------------------------+----------------------------+-------------------+------
 5 |            |           |       1 |    123 | testing photo upload | 2017-04-03 19:20:37.175447 | 2017-04-03 19:20:37.175447 | f                 | 0.00
 7 |            |           |       1 |    116 | testing large photo. | 2017-04-03 19:56:12.391366 | 2017-04-03 19:56:12.391366 | f                 | 0.00
13 |            |           |       1 |      1 | acl test             | 2017-04-04 07:35:59.974909 | 2017-04-04 07:35:59.974909 | f                 | 0.00
14 |            |           |       1 |    114 | rover1 upload\r     +| 2017-04-04 07:57:16.602674 | 2017-04-04 07:58:50.505527 | f                 | 0.00
16 |            |           |       1 |     54 |                      | 2017-04-04 08:53:29.394382 | 2017-04-04 08:53:29.394382 | f                 | 0.00

id | passed | user_id | ppe_id |         created_at         | advanced 
---+--------+---------+--------+----------------------------+----------
22 | f      |       7 |      6 | 2017-06-20 17:39:37.253423 | f
34 | f      |       1 |      4 | 2017-06-22 20:07:24.214546 | f
23 | f      |       9 |     20 | 2017-06-20 20:00:02.506964 | f
26 | t      |       5 |     42 | 2017-06-20 20:07:23.207904 | f
24 | t      |      10 |      4 | 2017-06-20 20:01:28.161158 | f

1 个答案:

答案 0 :(得分：1)

如果r_sub.ppe_id IS NULL，那么连接也将成为NULL ......

因为 SQL 中的几乎所有函数和操作都返回NULL，如果它的任何参数是NULL。 （NULL解释为“未知值”...）

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