带条件的内部连接-Mysql

如果条件为真但不起作用，我尝试进行内部联接，我尝试了以下两种方法：

IF chat.tipo = 'vitima' THEN
   INNER JOIN vitima ON vitima.id_vit = chat.id_tipo

ELSE
   INNER JOIN terceiro ON terceiro.id_ter = chat.id_tipo

或

但两者都给出了错误，我想要的是，如果类型等于vitima，它在一个表中做内部noin，否则在另一个表中

完整查询：

SELECT ocorrencia.id_oco, 
        (SELECT GROUP_CONCAT(c.id_oco ORDER BY c.id_oco DESC) FROM ocorrencia as c WHERE c.id_sup_oco = ocorrencia.id_sup_oco) as grouped_ids, 
        ocorrencia.id_sup_oco, 
        chat.id_tipo,
        suporte_oco.data_sup,
        suporte_oco.placa_sup,
        suporte_oco.sinistro_sup,
        suporte_oco.prefixo_sup,
        ocorrencia.id_emp_oco,
        IF(chat.tipo = 'vitima', vitima.nome_vit, terceiro.nome_ter) as nome,
        chat.tipo

        FROM chat 
        INNER JOIN ocorrencia ON ocorrencia.id_oco = chat.id_oco_cha 
        INNER JOIN suporte_oco ON suporte_oco.id_sup = ocorrencia.id_sup_oco

        IF chat.tipo = 'vitima'
            INNER JOIN vitima ON vitima.id_vit = chat.id_tipo
        ELSE
            INNER JOIN terceiro ON terceiro.id_ter = chat.id_tipo

        WHERE chat.id_user = '20' OR chat.id_user_req = '20' GROUP BY (chat.id_oco_cha) ORDER BY chat.data DESC

---

不能在联接中使用条件，可能更容易使用union，如：

我能想到的另一个变体是：

select *
from chat, vitima, terceiro
where
(chat.tipo = 'vitima' AND vitima.id_vit = chat.id_tipo)
OR
(chat.tipo <> 'vitima' AND terceiro.id_ter = chat.id_tipo)

---

这并不确切，但我认为这将非常接近您正在尝试做的事情：

LEFT JOIN vitima ON vitima.id_vit = chat.id_tipo AND chat.tipo = 'vitima'
LEFT JOIN terceiro ON terceiro.id_ter = chat.id_tipo AND chat.tipo != 'vitima'
...
WHERE (chat.tipo = 'vitima' AND vitima.id_vit IS NOT NULL)
    OR (chat.tipo != 'vitima' AND terceiro.id_ter IS NOT NULL)

左连接条件强制执行规则，WHERE条件模拟和内部连接，因为它要求这些记录存在

您发布的完整查询如下所示：

SELECT ocorrencia.id_oco, 
    (SELECT GROUP_CONCAT(c.id_oco ORDER BY c.id_oco DESC) FROM ocorrencia as c WHERE c.id_sup_oco = ocorrencia.id_sup_oco) as grouped_ids, 
    ocorrencia.id_sup_oco, 
    chat.id_tipo,
    suporte_oco.data_sup,
    suporte_oco.placa_sup,
    suporte_oco.sinistro_sup,
    suporte_oco.prefixo_sup,
    ocorrencia.id_emp_oco,
    IF(chat.tipo = 'vitima', vitima.nome_vit, terceiro.nome_ter) as nome,
    chat.tipo

FROM chat 
    INNER JOIN ocorrencia ON ocorrencia.id_oco = chat.id_oco_cha 
    INNER JOIN suporte_oco ON suporte_oco.id_sup = ocorrencia.id_sup_oco
    LEFT JOIN vitima ON vitima.id_vit = chat.id_tipo AND chat.tipo = 'vitima'
    LEFT JOIN terceiro ON terceiro.id_ter = chat.id_tipo AND chat.tipo != 'vitima'

WHERE chat.id_user = '20' OR chat.id_user_req = '20'
    AND (
        (chat.tipo = 'vitima' AND vitima.id_vit IS NOT NULL)
        OR (chat.tipo != 'vitima' AND terceiro.id_ter IS NOT NULL)
    )
GROUP BY (chat.id_oco_cha) ORDER BY chat.data DESC

---

我将把完整的查询放在这里让您查看，我在这里尝试过，但现在无法查看您的SQL“LEFT JOIN vitima ON vitima.id_vit=chat.id_tipo和chat.tipo=”vitima“L”在第17行出现语法错误谢谢，那里有一个错误的逗号。现在已经修好了。它起作用了：，只需在表vitimaoh上进行第一个内部连接，是的，我看到一个是双倍的。我能问一下，你有条件加入的目的是什么吗？既然你实际上没有从这些表中选择任何内容，你只是想确保存在相应的记录吗？@billynoah在那里我选择了字段，我也做了一个if，不知道它是否有效kkkkk，我想得到名称，请参见：IFchat.tipo='vitima'，vitima.nome_vit，terceiro.nome_ter as nomeah，这很有意义。在这种情况下，我认为在我的回答中使用左连接可能效果最好，因为您可能需要任何一个表中的一列。另一个选择是创建子查询——如果没有模式和示例数据，很难给出精确的解决方案，但我认为您已经接近了

LEFT JOIN vitima ON vitima.id_vit = chat.id_tipo AND chat.tipo = 'vitima'
LEFT JOIN terceiro ON terceiro.id_ter = chat.id_tipo AND chat.tipo != 'vitima'
...
WHERE (chat.tipo = 'vitima' AND vitima.id_vit IS NOT NULL)
    OR (chat.tipo != 'vitima' AND terceiro.id_ter IS NOT NULL)

SELECT ocorrencia.id_oco, 
    (SELECT GROUP_CONCAT(c.id_oco ORDER BY c.id_oco DESC) FROM ocorrencia as c WHERE c.id_sup_oco = ocorrencia.id_sup_oco) as grouped_ids, 
    ocorrencia.id_sup_oco, 
    chat.id_tipo,
    suporte_oco.data_sup,
    suporte_oco.placa_sup,
    suporte_oco.sinistro_sup,
    suporte_oco.prefixo_sup,
    ocorrencia.id_emp_oco,
    IF(chat.tipo = 'vitima', vitima.nome_vit, terceiro.nome_ter) as nome,
    chat.tipo

FROM chat 
    INNER JOIN ocorrencia ON ocorrencia.id_oco = chat.id_oco_cha 
    INNER JOIN suporte_oco ON suporte_oco.id_sup = ocorrencia.id_sup_oco
    LEFT JOIN vitima ON vitima.id_vit = chat.id_tipo AND chat.tipo = 'vitima'
    LEFT JOIN terceiro ON terceiro.id_ter = chat.id_tipo AND chat.tipo != 'vitima'

WHERE chat.id_user = '20' OR chat.id_user_req = '20'
    AND (
        (chat.tipo = 'vitima' AND vitima.id_vit IS NOT NULL)
        OR (chat.tipo != 'vitima' AND terceiro.id_ter IS NOT NULL)
    )
GROUP BY (chat.id_oco_cha) ORDER BY chat.data DESC