Mysql Query返回0結果

Question

給定這兩行中的值，為什么我的查詢返回0行，如何重寫查詢才能正常工作？

meta_id post_id meta_key   meta_value
   1422      73 wpcf-milk      22
   1423      73 wpcf-mw        -7

SQL查詢：

   SELECT * FROM wp_postmeta
    WHERE post_id = 73 
    AND ( meta_key = 'wpcf-mw' AND meta_value BETWEEN -8 AND 200 )
    AND ( meta_key = 'wpcf-milk' AND meta_value BETWEEN 20 AND 200 )

Answer 1

SELECT * FROM wp_postmeta 
WHERE post_id = 73 
  AND (( meta_key = 'wpcf-mw' AND meta_value BETWEEN -8 AND 200 ) 
  **OR** ( meta_key = 'wpcf-milk' AND meta_value BETWEEN 20 AND 200 ))

通過OR更改AND。

Answer 2

基本上有兩種方法可以做到這一點。 一個大致如下：

SELECT post_id
     , MAX(CASE WHEN meta_key = 'wpcf-milk' THEN meta_value END) wpcf_milk
     , MAX(CASE WHEN meta_key = 'wpcf-mw' THEN meta_value END) wpcf_mw 
  FROM wp_postmeta 
 GROUP 
    BY post_id 
HAVING wpcf_milk BETWEEN 20 AND 200 
   AND wpcf_mw BETWEEN -8 AND 200;

另一種方法涉及OUTER JOIN並且速度稍快，但輸入時稍微繁瑣一些 - 所以我會把它留給其他人。