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问从UNION set运算符中删除空值
EN

Stack Overflow用户

提问于 2019-09-09 06:38:08

回答 2查看 235关注 0票数 0

我们应该如何消除空值而不是将其保留在单独的行中，值必须驻留在列中，从而通过使用执行结果集中的联合集运算符使空值消失？

考虑一下简单的SQL查询。

SELECT
  *
FROM
  (
    (SELECT
      6 + 2 AS addition,
      NULL AS subtraction,
      NULL AS multiplication,
      NULL AS division
    FROM
      DUAL)
    UNION
    (SELECT
      NULL AS addition,
      6 - 2 AS subtraction,
      NULL AS multiplication,
      NULL AS division
    FROM
      DUAL)
    UNION
    (SELECT
      NULL AS addition,
      NULL AS subtraction,
      6 * 2 AS multiplication,
      NULL AS division
    FROM
      DUAL)
    UNION
    (SELECT
      NULL AS addition,
      NULL AS subtraction,
      NULL AS multiplication,
      6 / 2 AS division
    FROM
      DUAL)
  ) A;

实际结果：

+----------+-------------+----------------+----------+
| addition | subtraction | multiplication | division |
+----------+-------------+----------------+----------+
|        8 |        NULL |          NULL  |     NULL |
|     NULL |           4 |          NULL  |     NULL |
|     NULL |        NULL |            12  |     NULL |
|     NULL |        NULL |          NULL  |   3.0000 |
+----------+-------------+----------------+----------+
4 rows in set (0.00 sec)

预期结果：

+----------+-------------+----------------+----------+
| addition | subtraction | multiplication | division |
+----------+-------------+----------------+----------+
|        8 |           4 |          12    |   3.0000 |
+----------+-------------+----------------+----------+
1 row in set (0.00 sec)

SQL Demo

union

sql-null

mysql

sql

mariadb

回答 2

Stack Overflow用户

回答已采纳

发布于 2019-09-09 06:39:23

你可以在下面试试-

SELECT
  max(addition) as addition,max(subtraction) as subtraction, max(multiplication) as multiplication,max(division) as division
FROM
  (
    (SELECT
      6 + 2 AS addition,
      NULL AS subtraction,
      NULL AS multiplication,
      NULL AS division
    FROM
      DUAL)
    UNION
    (SELECT
      NULL AS addition,
      6 - 2 AS subtraction,
      NULL AS multiplication,
      NULL AS division
    FROM
      DUAL)
    UNION
    (SELECT
      NULL AS addition,
      NULL AS subtraction,
      6 * 2 AS multiplication,
      NULL AS division
    FROM
      DUAL)
    UNION
    (SELECT
      NULL AS addition,
      NULL AS subtraction,
      NULL AS multiplication,
      6 / 2 AS division
    FROM
      DUAL)
  ) A;

票数 1

Stack Overflow用户

发布于 2019-09-09 07:47:48

这个应该行。

SELECT
 sum(isnull(addition,0)) addition
 ,sum(isnull(subtraction,0)) subtraction
 ,sum(isnull(multiplication,0)) multiplication
 ,sum(isnull(division,0)) division
FROM
  (
    (SELECT
      6 + 2 AS addition,
      NULL AS subtraction,
      NULL AS multiplication,
      NULL AS division
    )
    UNION
    (SELECT
      NULL AS addition,
      6 - 2 AS subtraction,
      NULL AS multiplication,
      NULL AS division
    )
    UNION
    (SELECT
      NULL AS addition,
      NULL AS subtraction,
      6 * 2 AS multiplication,
      NULL AS division
    )
    UNION
    (SELECT
      NULL AS addition,
      NULL AS subtraction,
      NULL AS multiplication,
      6 / 2 AS division
    )
  ) A

票数 1

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/57848916

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