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我可能在这里遗漏了一些明显的东西。我有一个 WordPress 分类法，它parent通过wp_term_taxonomy. 我正在尝试编写一个查询，该查询将返回一行，无论是否存在子区域（仍返回县）。在此示例中，我正在查询我知道数据库中存在的区域 ('PHILADELPHIA') 以及我知道不存在的子区域 ('asdfasdfasdf')。如果我将“asdfasdfasdf”更改为我知道存在的子区域，则该行返回正常，但如果该子区域不存在，我不会在 RIGHT 表中得到 NULL（没有行返回，就好像它在做一个内部连接）。这是查询：

SELECT region_wtt.term_taxonomy_id AS region_ttid,
    region_wtt.term_id AS region_tid,
    region_wt.name AS region_name,
    subregion_wtt.term_taxonomy_id AS subregion_ttid,
    subregion_wtt.term_id AS subregion_tid,
    subregion_wt.name AS subregion_name

FROM wp_term_taxonomy region_wtt

RIGHT OUTER JOIN wp_term_taxonomy subregion_wtt
ON region_wtt.term_taxonomy_id = subregion_wtt.parent

RIGHT OUTER JOIN wp_terms region_wt
ON region_wtt.term_id = region_wt.term_id

RIGHT OUTER JOIN wp_terms subregion_wt
ON subregion_wtt.term_id = subregion_wt.term_id

WHERE region_wtt.taxonomy='tsml_region'
    AND region_wtt.parent = 0
    AND region_wt.name='PHILADELPHIA'
    AND subregion_wtt.taxonomy='tsml_region'
    AND subregion_wt.name='asdfasdfasdf';

我错过了什么？

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