为什么组合顺序是重要的？内连接？
以下失败与postgres：
以下失败与postgres：
SELECT grp.number AS number,tags.value AS tag
FROM groups grp,insrel archiverel
LEFT OUTER JOIN ownrel ownrel ON grp.number = ownrel.dnumber
LEFT OUTER JOIN tags tags ON tags.number = ownrel.snumber
WHERE archiverel.snumber = 11128188 AND
archiverel.dnumber = grp.number
结果是：
ERROR: invalid reference to FROM-clause entry for table "grp" LINE 5: LEFT OUTER JOIN ownrel ownrel ON grp.number = ownrel.d... ^ HINT: There is an entry for table "grp",but it cannot be referenced from this part of the query.
当这些组在FROM中相反时，它们都可以工作：
SELECT grp.number AS number,tags.value AS tag
FROM insrel archiverel,groups grp
LEFT OUTER JOIN ownrel ownrel ON grp.number = ownrel.dnumber
LEFT OUTER JOIN tags tags ON tags.number = ownrel.snumber
WHERE archiverel.snumber = 11128188 AND
archiverel.dnumber = grp.number
我相信你可以把它看作一个运算符优先级问题。
原文链接：https://www.f2er.com/postgresql/192946.html当你写这个：
FROM groups grp,insrel archiverel LEFT OUTER JOIN ownrel ownrel ON grp.number = ownrel.dnumber LEFT OUTER JOIN tags tags ON tags.number = ownrel.snumber
我认为解析器是这样解释的：
FROM groups grp,(
(
insrel archiverel
LEFT OUTER JOIN ownrel ownrel ON grp.number = ownrel.dnumber
)
LEFT OUTER JOIN tags tags ON tags.number = ownrel.snumber
)
如果是这样，那么在最内层的连接“grp”是没有绑定的。
当您使用“groups”和“insrel”反转行时，最内层的连接适用于“groups”和“ownrel”，因此它可以正常工作。
这可能也会奏效：
FROM groups grp
JOIN insrel archiverel ON archiverel.dnumber = grp.number
LEFT OUTER JOIN ownrel ownrel ON grp.number = ownrel.dnumber
LEFT OUTER JOIN tags tags ON tags.number = ownrel.snumber
WHERE archiverel.snumber = 11128188
