Question

我正在尝试将多个表的LEFT JOIN用作单个表：

SELECT unit.unit_id,
       unit_situation_legal_protection.unit_situation_legal_protection_id,
       situation.situation_id,
       situation.situation_type,
       legal.legal_id,
       legal.legal_type,
       protection.protection_id,
       protection.protection_type,
       unit_situation_legal_protection.unit_situation_legal_protection_date_added,
       unit_situation_legal_protection.unit_situation_legal_protection_status
FROM unit
LEFT JOIN unit_situation_legal_protection ON unit.unit_id = unit_situation_legal_protection.unit_id
LEFT JOIN situation ON unit_situation_legal_protection.situation_id= situation.situation_id
LEFT JOIN legal ON unit_situation_legal_protection.legal_id = legal.legal_id
LEFT JOIN protection ON unit_situation_legal_protection.protection_id=protection.protection_id
WHERE unit_situation_legal_protection.unit_id = 146

我需要从各自的表中获取legal_type，protection_type和situation_type，并将它们添加到返回的行中。

我可以从结果中获得legal_id，protection_id和situation_id，但是legal_type，protection_type和situation_type始终为空

编辑：说明

有5张桌子：

主要的unit表和通过unit_situation_legal_protection连接到unit作为外键的unit_id。

unit_situation_legal_protection具有其他外键，例如legal_id，protection_id和situation_id。它们的每个表都有一个单独的表，其中包含id和type。

因此情况表包含：situation_id和situation_type。

Answer 1

WHERE unit_situation_legal_protection.unit_id = 146从您的join中产生left join。删除where子句并将其添加到联接中：

SELECT unit.unit_id,
       unit_situation_legal_protection.unit_situation_legal_protection_id,
       situation.situation_id,
       situation.situation_type,
       legal.legal_id,
       legal.legal_type,
       protection.protection_id,
       protection.protection_type,
       unit_situation_legal_protection.unit_situation_legal_protection_date_added,
       unit_situation_legal_protection.unit_situation_legal_protection_status
FROM unit
LEFT JOIN unit_situation_legal_protection ON unit.unit_id = unit_situation_legal_protection.unit_id and unit_situation_legal_protection.unit_id = 146
LEFT JOIN situation ON unit_situation_legal_protection.situation_id= situation.situation_id
LEFT JOIN legal ON unit_situation_legal_protection.legal_id = legal.legal_id
LEFT JOIN protection ON unit_situation_legal_protection.protection_id=protection.protection_id

使用多个表的左联接到一个表时，MySQL Query无法获得结果

1 个答案: