我正在查询一个对自身具有嵌套引用的表,并且我需要获取对我正在使用的 INNER JOIN 值有空引用的记录。换句话说,树表记录可能不会达到相同的深度,我需要全部获取。
我正在使用 atm 的查询是:
SELECT DISTINCT <valuesThatINeed>
FROM atable foo
INNER JOIN treetable bar ON foo.id_bar = bar.id
INNER JOIN treetable bar2 ON bar.id_bar = bar2.id
INNER JOIN treetable bar3 ON bar2.id_bar = bar3.id
WHERE
<constraints>
我读过我可以通过添加一个 OR 语句来扩展 INNER JOIN 条件,询问 bar.id_bar 是否为 NULL,但如果我这样做,我将无法达到更高的水平:
SELECT DISTINCT <valuesThatINeed>
FROM atable foo
INNER JOIN treetable bar ON foo.id_bar = bar.id
INNER JOIN treetable bar2 ON bar.id_bar = bar2.id OR (bar.id_bar IS NULL)
INNER JOIN treetable bar3 ON bar2.id_bar = bar3.id
WHERE
<constraints>