如何在 MySQL 中 FULL OUTER JOIN 多个表

Posted 2023-02-24

【中文标题】如何在 MySQL 中 FULL OUTER JOIN 多个表

【英文标题】：How to FULL OUTER JOIN multiple tables in MySQL

【发布时间】：2015-08-10 09:51:21

【问题描述】：

我需要FULL OUTER JOIN 多个表。我知道如何FULL OUTER JOIN 来自here 的两个表。但是我有几张桌子，我不能在它们上面应用它。我怎样才能实现它？ 我的 SQL 代码，如下：

INSERT INTO table
(
  customer_id
 ,g01
 ,g02
 ,g03
 ,has_card
 ,activity
  )
  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  LEFT JOIN s_category sc
  ON sc.customer_id = sgd.customer_id
    UNION
  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  RIGHT JOIN s_category sc
  ON sc.customer_id = sgd.customer_id

    UNION

  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  LEFT JOIN s_activity a
  ON a.customer_id = sgd.customer_id
    UNION
  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  RIGHT JOIN s_activity a
  ON a.customer_id = sgd.customer_id

我也试过这个查询：

INSERT INTO reportls.table
(
  customer_id
 ,g01
 ,g02
 ,g03
 ,has_card
 ,activity
  )
  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  LEFT JOIN s_category sc
  ON sc.customer_id = sgd.customer_id
  LEFT JOIN s_activity a
  ON sc.customer_id = sgd.customer_id

    UNION

  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  LEFT JOIN s_category sc
  ON sc.customer_id = sgd.customer_id
  RIGHT JOIN s_activity a
  ON a.customer_id = sgd.customer_id

    UNION

  SELECT sgd.customer_id, sgd.g01,sgd.g02,sgd.g03,sc.value, a.activity
  FROM s_geo_data sgd
  RIGHT JOIN s_category sc
  ON sc.customer_id = sgd.customer_id
  LEFT JOIN s_activity a
  ON a.customer_id = sgd.customer_id

最后一个查询执行时间很长，我需要更快的查询。

【参考方案1】：

我认为有一个FULL OUTER JOIN 超过 3 个表，你需要这样做：

SELECT t1.value, t2.value, t3.value
FROM t1 LEFT JOIN t2 ON t1.value = t2.value
        LEFT JOIN t3 ON t1.value = t3.value
UNION ALL
SELECT t1.value, t2.value, t3.value
FROM t2 LEFT JOIN t1 ON t1.value = t2.value
        LEFT JOIN t3 ON t2.value = t3.value
WHERE t1.value IS NULL
UNION ALL
SELECT t1.value, t2.value, t3.value
FROM t3 LEFT JOIN t1 ON t1.value = t3.value
        LEFT JOIN t2 ON t2.value = t3.value
WHERE t1.value IS NULL AND t2.value IS NULL

作为替代方案：

SELECT t1.value, t2.value, t3.value
FROM t1 FULL OUTER JOIN t2 ON t1.value = t2.value
        FULL OUTER JOIN t3 ON t1.value = t3.value

---

我建议您创建一些临时表，如 t1、t2 和 t3 来存储查询结果，然后使用上述查询。

【讨论】：

我执行您的查询，等待 20 多分钟，然后按取消。 ))

@ШыназАлиш 20 分钟真的很高，但我想不出更好的查询 ;)。

@感谢您的回复！！

为什么要写 UNION ALL 而不是 UNION？

对于 FULL OUTER JOINing n 表来说，这如何扩展？