php - 我可以排除复杂查询中满足条件的行吗？ (组合 WHERE + 多重 AND)

Question

我需要从表中获取结果，其中分组 ID 存在于 field1 = a 且 field2 IS NOT NULL 的行中，但不存在 field1 = b 且 field2 IS NOT NULL 的行中。只是出现语法错误，不太知道如何组合这些标准...

这就是我正在尝试做的事情:

SELECT a.post_title AS title, a.id,
     MAX(CASE WHEN b.meta_key = 'endorser' THEN b.meta_value END) endorser,
     MAX(CASE WHEN b.meta_key = 'trail' THEN b.meta_value END) trail,
     MAX(CASE WHEN b.meta_key = 'townarea' THEN b.meta_value END) townarea,
     MAX(CASE WHEN b.meta_key = 'state' THEN b.meta_value END) state,
     MAX(CASE WHEN b.meta_key = 'start-date' THEN b.meta_value END) startdate,
     MAX(CASE WHEN b.meta_key = 'description' THEN b.meta_value END) description,
     MAX(CASE WHEN b.meta_key = 'organizer-name' THEN b.meta_value END) organizer,
     MAX(CASE WHEN b.meta_key = 'info-email' THEN b.meta_value END) infoemail
     FROM wp_posts a LEFT JOIN wp_postmeta b ON a.id = b.post_id
     WHERE b.post_id IN 
        (SELECT Post_id FROM wp_postmeta 
         WHERE (meta_key = 'endorser' AND meta_value IS NOT NULL) 
         AND (meta_key = 'trail' AND meta_value IS NULL)) group by b.post_id

表格看起来像这样:

meta_id  |   post_id   |  meta_key  |   meta_value
---------|-------------|------------|------------
  1      |     53      |  endorser  |   joe
  2      |     54      |  trail     |   trail name

所以我会得到包含 post_id 53 的行，但不是 54

我很累，所以我可能会错过一些简单的东西，比如简单的 OUTER JOIN？

这是 fiddle :http://sqlfiddle.com/#!2/ee5420/1

Answer 1

您可以使用 b.meta_key IN ('endorser','trail') 来摆脱子查询，并且在 where 子句中您可以使用 CASE 作为您的 is为 null 且不为 null 条件

SELECT a.post_title AS title, a.id,
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'endorser' AND post_id =a.id) endorser,
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'trail' AND post_id =a.id) trail,   
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'townarea' AND post_id =a.id) townarea,   
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'state' AND post_id =a.id) state,   
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'start-date' AND post_id =a.id) startdate,   
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'description' AND post_id =a.id) description,   
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'organizer-name' AND post_id =a.id) organizer,   
(SELECT MAX(meta_value) FROM wp_postmeta WHERE meta_key = 'info-email' AND post_id =a.id) infoemail   
     FROM wp_posts a 
     LEFT JOIN wp_postmeta b ON a.id = b.post_id
 WHERE b.meta_key  IN ('endorser','trail')
     AND (
  CASE
    WHEN b.meta_key = 'endorser' 
    THEN b.meta_value IS NOT NULL 
    WHEN b.meta_key = 'trail' 
    THEN b.meta_value IS NULL 
  END
)
HAVING trail =''

Fiddle Demo