Sql 如何计算每列中有多少空值？

我有一张这样的桌子：

col1

col2

col3

1

0

null

null

null

null

3

null

null

null

5

1

我希望在Oracle 10G中有这样的输出：

列名称

空计数

col1

2

col2

2

col3

3

我使用UNION ALL实现了这一点，如下所示：

select "col1" column_name,sum(case when col1 is null then 1 else 0 end) as null_count from A group by "col1"
union all
select "col2" column_name,sum(case when col2 is null then 1 else 0 end) as null_count from A group by "col2"
union all
select "col3" column_name,sum(case when col3 is null then 1 else 0 end) as null_count from A group by "col3";

它工作正常，但需要花费大量时间，因为有近100个工会会员。我希望实现相同的输出，而不使用UNION ALL

是否有任何方法可以在不使用UNION ALL的情况下实现这一点

---

你可以使用UNPIVOT（我不确定古代甲骨文10是否已经支持了这一点——我已经十多年没有使用过了）

但不确定这是否更快

---

联机示例：

Oracle 10g不支持取消PIVOT和PIVOT运算符，因此要在10g中执行您所追求的操作，您需要使用一个虚拟表（包含与取消PIVOT的列相同的行数-在您的示例中，为3），如下所示：

WITH your_table AS (SELECT 1 col1, 0 col2, NULL col3 FROM dual UNION ALL
                    SELECT NULL col1, NULL col2, NULL col3 FROM dual UNION ALL
                    SELECT 3 col1, NULL col2, NULL col3 FROM dual UNION ALL
                    SELECT NULL col1, 5 col2, 1 col3 FROM dual)
SELECT CASE WHEN dummy.id = 1 THEN 'col1'
            WHEN dummy.id = 2 THEN 'col2'
            WHEN dummy.id = 3 THEN 'col3'
       END column_name,
       COUNT(CASE WHEN dummy.id = 1 THEN CASE WHEN col1 IS NULL THEN 1 END
                  WHEN dummy.id = 2 THEN CASE WHEN col2 IS NULL THEN 1 END
                  WHEN dummy.id = 3 THEN CASE WHEN col3 IS NULL THEN 1 END
             END) null_count
FROM   your_table
       CROSS JOIN (SELECT LEVEL ID
                   FROM   dual
                   CONNECT BY LEVEL <= 3) dummy
GROUP BY dummy.id;

COLUMN_NAME NULL_COUNT
----------- ----------
col1                 2
col2                 2
col3                 3

---

（我使用了

行编号（）

分析函数，而不是使用列id，因为如果排除某些列，列id列将不再是从1开始的连续数字。）

谢谢，这正是我要查找的。但当列的数据类型不同时，这会导致问题。

WITH your_table AS (SELECT 1 col1, 0 col2, NULL col3 FROM dual UNION ALL
                    SELECT NULL col1, NULL col2, NULL col3 FROM dual UNION ALL
                    SELECT 3 col1, NULL col2, NULL col3 FROM dual UNION ALL
                    SELECT NULL col1, 5 col2, 1 col3 FROM dual)
SELECT CASE WHEN dummy.id = 1 THEN 'col1'
            WHEN dummy.id = 2 THEN 'col2'
            WHEN dummy.id = 3 THEN 'col3'
       END column_name,
       COUNT(CASE WHEN dummy.id = 1 THEN CASE WHEN col1 IS NULL THEN 1 END
                  WHEN dummy.id = 2 THEN CASE WHEN col2 IS NULL THEN 1 END
                  WHEN dummy.id = 3 THEN CASE WHEN col3 IS NULL THEN 1 END
             END) null_count
FROM   your_table
       CROSS JOIN (SELECT LEVEL ID
                   FROM   dual
                   CONNECT BY LEVEL <= 3) dummy
GROUP BY dummy.id;

COLUMN_NAME NULL_COUNT
----------- ----------
col1                 2
col2                 2
col3                 3

SELECT 'when dummy.id = '||row_number() OVER (PARTITION BY owner, table_name ORDER BY column_id)||' then '''||LOWER(column_name)||'''' first_part,
       'when dummy.id = '||row_number() OVER (PARTITION BY owner, table_name ORDER BY column_id)||' then case when '||column_name||' is null then 1 end' second_part
FROM   all_tab_columns a
WHERE  owner = ...
AND    table_name = ...
-- and column_name in (...)
ORDER BY column_id;