MySQL连接问题

有谁能告诉我，是否可以使用自连接将以下两个查询合并为一个查询，如果可以，如何实现

问题1：

   SELECT pm.username AS user,
          uc.content_id AS id,
          value AS filename,
          name,
          moderation_status AS status,
          uc.parent_content_id
     FROM myweb.ugc_meta um
LEFT JOIN myweb.ugc_content uc ON uc.content_id = um.item_id
LEFT JOIN myweb.userbase_member pm ON uc.user_id = pm.id
    WHERE uc.content_type ='my.photo'
      AND uc.promoted = '1'
      AND moderation_status='passed'
    LIMIT 10

问题2：

SELECT value
  FROM myweb.ugc_meta um
 WHERE um.item_id = '4780c650137a3409901286'
-- (item_id is the content_parent_id from query 1)

ugc\u meta

包含

ugc\u content

中照片的相册名称<代码>ugc_内容包含相册和照片的行<代码>代表照片的行有一个

父内容id

，它是父行的

内容id

。我没有更改表或数据库结构的选项

目前，我正在为查询1中的每一个次优结果行运行一个新查询（查询2；-）

---

谢谢

如果要自联接表，必须为每个表指定不同的别名，那么它应该可以正常工作

   SELECT pm.username AS user,
          uc.content_id AS id,
          um.value AS filename, um2.value AS filename2
          um.name, um2.name AS name2
          moderation_status AS status,
          uc.parent_content_id
     FROM myweb.ugc_meta um
LEFT JOIN myweb.ugc_content uc
       ON uc.content_id = um.item_id
LEFT JOIN myweb.userbase_member pm
       ON uc.user_id = pm.id
LEFT JOIN myweb.ugc_meta um2
       ON id = um2.item_id
    WHERE uc.content_type ='my.photo'
      AND uc.promoted = '1'
      AND moderation_status='passed'
    LIMIT 10

---

希望这能奏效

您应该能够使用不同的别名简单地使用到ugc_元表的左联接，以实现父表联接，如下所示：

SELECT pm.username AS user,
          uc.content_id AS id,
          value AS filename,
          name,
          moderation_status AS status,
          uc.parent_content_id,
          parent.`value`
     FROM myweb.ugc_meta um
LEFT JOIN myweb.ugc_content uc ON uc.content_id = um.item_id
LEFT JOIN myweb.ugc_meta parent ON uc.parent_content_id = parent.item_id
LEFT JOIN myweb.userbase_member pm ON uc.user_id = pm.id
    WHERE uc.content_type ='my.photo'
      AND uc.promoted = '1'
      AND moderation_status='passed'
    LIMIT 10

我使用左连接是因为子表中可能不总是有父级内容id，如果在这种情况下总是有父级内容id，那么您可以使用内部连接，这将进一步提高性能。

这应该可以做到：

SELECT pm.username AS user,
      uc.content_id AS id,
      value AS filename, 
      name,
      moderation_status AS status,
      um2.value AS 
FROM myweb.ugc_meta um
LEFT JOIN myweb.ugc_content uc ON uc.content_id = um.item_id
LEFT JOIN myweb.userbase_member pm ON uc.user_id = pm.id
LEFT JOIN myweb.ugc_meta om2 ON um2.item_id = uc.parent_content_id
WHERE uc.content_type ='my.photo'
  AND uc.promoted = '1'
  AND moderation_status='passed'
LIMIT 10

如果它们来自ugc\U meta，您可能必须在

值

、

名称

和

适度状态

前面加上“um.”，否则该值是否取自

um

og

um2

，就会模糊不清