Question

我有这个SQL语句

SELECT
    locales.id_c,
    locales.name_p AS NombrePropietario,
    locales.surname1 AS PrimerApellido,
    locales.local_name AS Nombre_Local,
    locales.zona AS ZonaLiga,
    locales.id_m1 AS Maquina_1,
    maquinas.tipo_m AS Tipo_de_Maquina1,
    locales.id_m2 AS Maquina_2,
    maquinas.tipo_m AS Tipo_de_Maquina2,
    locales.id_m3 AS Maquina_3,
    locales.id_m4 AS Maquina_4
FROM locales
INNER JOIN maquinas
    ON locales.id_m1 = maquinas.id_m;

在这种情况下，它只显示了＆＃34; Maquina_1＆＃34;和＆＃34; Tipo_de_Maquina1＆＃34;

并且需要展示＆＃34; Maquina_2＆＃34;和＆＃34; Tipo_de_Maquina2＆＃34;，＆＃34; Maquina_3＆＃34;和＆＃34; Tipo_de_Maquina3＆＃34;等等。

有人可以帮助我吗？

由于

Answer 1

使用表别名加入maqinas表格多重：

SELECT
  l.id_c,
  l.name_p AS NombrePropietario,
  l.surname1 AS PrimerApellido,
  l.local_name AS Nombre_Local,
  l.zona AS ZonaLiga,
  l.id_m1 AS Maquina_1,
  m1.tipo_m AS Tipo_de_Maquina1,
  l.id_m2 AS Maquina_2,
  m2.tipo_m AS Tipo_de_Maquina2,
  l.id_m3 AS Maquina_3,
  m3.tipo_m AS Tipo_de_Maquina3,
  l.id_m4 AS Maquina_4,
  m4.tipo_m AS Tipo_de_Maquina4
FROM locales l
LEFT JOIN maquinas m1 ON l.id_m1 = m1.id_m
LEFT JOIN maquinas m2 ON l.id_m2 = m2.id_m
LEFT JOIN maquinas m3 ON l.id_m3 = m3.id_m
LEFT JOIN maquinas m4 ON l.id_m4 = m4.id_m
;

如果记录没有maquina 1,2,3或4，我正在使用外部联接。如果每条记录都有所有maquinas，则可以切换到内部联接。

无论如何，您可能需要考虑另一个数据模型，在其中添加表locale_maquina并从id_m1表中删除单个id_m4到locales。这样可以更轻松地选择数据并支持链接到某个位置的灵活数量的maquinas。

Answer 2

您的“Tipo_de_Maquina2”错误，因为它会显示“Tipo_de_Maquina1”的相同值。

您应该遵循“Tipo_de_Maquina1”的相同INNER JOIN逻辑，以获取tipo_m的其他值。

SELECT
    locales.id_c,
    locales.name_p AS NombrePropietario,
    locales.surname1 AS PrimerApellido,
    locales.local_name AS Nombre_Local,
    locales.zona AS ZonaLiga,
    locales.id_m1 AS Maquina_1,
    m1.tipo_m AS Tipo_de_Maquina1,
    locales.id_m2 AS Maquina_2,
    m2.tipo_m AS Tipo_de_Maquina3,
    locales.id_m3 AS Maquina_3,
    m3.tipo_m AS Tipo_de_Maquina4,
    locales.id_m4 AS Maquina_4,
    m4.tipo_m AS Tipo_de_Maquina4
FROM locales
INNER JOIN maquinas AS m1
    ON locales.id_m1 = m1.id_m
INNER JOIN maquinas AS m2
    ON locales.id_m2 = m2.id_m
INNER JOIN maquinas AS m3
    ON locales.id_m3 = m3.id_m
INNER JOIN maquinas AS m4
    ON locales.id_m4 = m4.id_m;

MySQL语句内连接

2 个答案: