左自连接 return 每 'primary' 一行

Question

我有一个 table 看起来像这样：

Rel_Id  Last    First   Relation
1   Jones   John    Primary
1   Jones   Mary    Spouse
1   Jones   Carl    Dependent
2   Will    Bill    Primary
3   Fine    Howard  Primary
4   Smith   Diana   Primary
4   Smith   Axel    Spouse

我正在尝试 return 所有 "Primary" 关系，每行一个，但如果有配偶，则将配偶包括在同一行。

我想要实现的结果如下所示：

1   Jones   John    Primary Jones   Mary    Spouse
2   Will    Bill    Primary null    null    null
3   Fine    Howard  Primary null    null    null
4   Smith   Diana   Primary Smith   Axel    Spouse

或者这样也行:

1   Jones   John    Primary Jones   Mary    Spouse
2   Will    Bill    Primary Will    Bill    Primary
3   Fine    Howard  Primary Fine    Howard  Primary
4   Smith   Diana   Primary Smith   Axel    Spouse

这是我的查询：

SELECT
P.Rel_Id,
P.Last,
P.`First`,
P.Relation,
S.Last AS sLast,
S.`First` AS sFirst,
S.Relation AS sRelation
FROM
relations AS P
LEFT JOIN relations AS S ON S.Rel_Id = P.Rel_Id
WHERE P.Relation = 'Primary' 
AND S.Relation <> 'Dependent'

以上查询结果为：

1   Jones   John    Primary Jones   John    Primary
1   Jones   John    Primary Jones   Mary    Spouse
2   Will    Bill    Primary Will    Bill    Primary
3   Fine    Howard  Primary Fine    Howard  Primary
4   Smith   Diana   Primary Smith   Diana   Primary
4   Smith   Diana   Primary Smith   Axel    Spouse

不幸的是，我的查询在正确排除“Dependent”的同时显示了两行唯一 'Primary' 成员，其中有一个配偶，我不想要。我如何 return 每个 'Primary' 只和配偶有关系吗？

Answer 1

您需要在联接条件中的查询中添加一个额外的检查，以便不显示两个主节点，只显示配偶。

所以在查询中也加上这个条件：

S.Relation <> P.Relation

因此最终查询将变为：

SELECT
P.Rel_Id,
P.Last,
P.`First`,
P.Relation,
S.Last AS sLast,
S.`First` AS sFirst,
S.Relation AS sRelation
FROM
relations AS P
LEFT JOIN relations AS S ON S.Rel_Id = P.Rel_Id AND S.Relation <> P.Relation
WHERE P.Relation = 'Primary' 
AND S.Relation <> 'Dependent'

希望对您有所帮助。

Answer 2

SELECT  GROUP_CONCAT(CONCAT_WS(' ',
                               last, first, relation),
                     SEPARATOR ' -- '
                     ORDER BY IF(relation = 'PRIMARY', 0, rel_id)
        ) AS Family
    FROM relations
    GROUP BY last;

它不会像您要求的那样给您 "columns"，但它可能会。

这将处理任何人数的家庭。但是，这取决于 last 是唯一的。（这是您的架构设计中存在的缺陷。）

将 last 分开可能更好：

SELECT  last,
        GROUP_CONCAT(CONCAT_WS(' ',
                               first, relation),
                     SEPARATOR ' -- '
                     ORDER BY IF(relation = 'PRIMARY', 0, rel_id)
        ) AS Family
    FROM relations
    GROUP BY last;

Answer 3

现在这看起来很明显 - 而且很简单！（谢谢大家 - 真的）

SELECT
P.Rel_Id,
P.Last,
P.`First`,
P.Relation,
S.Rel_Id AS sRel_Id,
S.Last AS sLast,
S.`First` AS sFirst,
S.Relation AS sRelation
FROM
relations AS P
LEFT JOIN relations AS S ON S.Rel_Id = P.Rel_Id and S.Relation = 'Spouse'
WHERE P.Relation = 'Primary'

左自连接 return 每 'primary' 一行

Left Self Join return one row per 'primary'

mysql

mariadb