Question

我需要将2列合并为1行。列之间的关键是post_id。

这是我的表（postmeta）：

post_id     meta_key    meta_value
36          cp_state    California
37          cp_state    Illinois
38          cp_state    California
39          cp_state    California
40          cp_state    California
36          cp_city     Los Angeles
37          cp_city     Chicago
38          cp_city     San Diego
39          cp_city     San Diego
40          cp_city     Los Angeles

以下是我试图输出的内容：

post_id     state       city
36          California  Los Angeles
37          Illinois    Chicago
38          California  San Diego
39          California  San Diego
40          California  Los Angeles

这是我使用的SQL，但得到了大量的结果：

SELECT a.post_id AS pID, a.meta_value AS state, b.meta_value AS city
FROM $wpdb->prefix"."postmeta AS a
LEFT JOIN $wpdb->prefix"."postmeta AS b
ON b.post_id = a.post_id
WHERE a.meta_key = 'cp_state'
AND b.meta_key = 'cp_city'

在我使用的直播Wordpress表中，显然有数百个其他meta_key，所以我需要它来过滤这两个meta_key（cp_city，cp_state）

Answer 1

您应该使用INNER JOIN而不是LEFT JOIN

SELECT a.post_id AS pID, a.meta_value AS state, b.meta_value AS city
FROM       $wpdb->prefix"."postmeta AS a
INNER JOIN $wpdb->prefix"."postmeta AS b
ON b.post_id = a.post_id
WHERE a.meta_key = 'cp_state'
AND b.meta_key = 'cp_city'

SQL JOIN在同一个表上有2个条件

1 个答案: