如何仅检索Oracle中任何行中至少具有一个非空值的列

Question

我的表结构和数据如下 https://ibb.co/mkGp67

我想要一个 SQL 查询只为那些至少有一个非空值的列检索数据，在上述情况下，我希望数据出来

https://ibb.co/mz9967

即我不需要 Col2、Col5 和 Col6 列，而且哪一列全为空值也不固定。

请让我知道 SQL 查询，它检索的数据只有那些不具有上述数据的空值的列。

Answer 1

据我所知，您无法通过 SQL 查询来实现这一点。 SELECT 语句的强假设之一是返回的列列表是静态的 - 在查询中定义，而不是由数据定义。即使对于 PIVOT 查询（据我所知，自 Oracle 11 以来可用），列列表也是在查询中定义的，通过提供要转换为列的值列表，必须明确给出。

您正在寻找的是某种代码，动态生成查询。这可以是 PL/SQL，返回游标引用或任何应用程序代码。

编辑：

您可以对查询做的事情是清楚地了解哪些列包含空值，哪些列不包含空值等。它可能看起来像这样：

SELECT CASE
         WHEN COUNT(*) = 0 THEN 'no rows'
         WHEN COUNT(Col1) = 0 THEN 'all NULLs'
         WHEN COUNT(Col1) = COUNT(*) THEN 'no NULLs'
         ELSE 'some NULLs'
       END Col1NullStatus,
       CASE
         WHEN COUNT(*) = 0 THEN 'no rows'
         WHEN COUNT(Col2) = 0 THEN 'all NULLs'
         WHEN COUNT(Col2) = COUNT(*) THEN 'no NULLs'
         ELSE 'some NULLs'
       END Col2NullStatus,
       CASE
         WHEN COUNT(*) = 0 THEN 'no rows'
         WHEN COUNT(Col3) = 0 THEN 'all NULLs'
         WHEN COUNT(Col3) = COUNT(*) THEN 'no NULLs'
         ELSE 'some NULLs'
       END Col3NullStatus,
       CASE
         WHEN COUNT(*) = 0 THEN 'no rows'
         WHEN COUNT(Col4) = 0 THEN 'all NULLs'
         WHEN COUNT(Col4) = COUNT(*) THEN 'no NULLs'
         ELSE 'some NULLs'
       END Col4NullStatus,
       CASE
         WHEN COUNT(*) = 0 THEN 'no rows'
         WHEN COUNT(Col5) = 0 THEN 'all NULLs'
         WHEN COUNT(Col5) = COUNT(*) THEN 'no NULLs'
         ELSE 'some NULLs'
       END Col5NullStatus,
       CASE
         WHEN COUNT(*) = 0 THEN 'no rows'
         WHEN COUNT(Col6) = 0 THEN 'all NULLs'
         WHEN COUNT(Col6) = COUNT(*) THEN 'no NULLs'
         ELSE 'some NULLs'
       END Col6NullStatus
  FROM myTable

见SQL Fiddle for the above。

编辑 2：

这个查询的输出看起来像这样：

Col1Null状态 | Col2Null状态 | Col3NullStatus | Col4Null状态 | Col5NullStatus | Col6NullStatus ---------------+----------------+----------------+ ----------------+----------------+---------------- 没有空值 |所有 NULL |一些空值 |没有空值 |所有 NULL |所有 NULL

这是您可以用来发布输入数据和预期结果的格式。

Answer 2

因此，由于您没有给出正式的表结构，而且您似乎混淆了数字和字符，因此我会尽力尝试进行查询，至少会产生您想要的结果。

创建表 foo 为 ( col1 varchar(10), col2 varchar(10), col3 varchar(10), col4 varchar(10), col5 varchar(10), col6 varchar(10) );

选择 * CASE cust1 WHEN null then 'null' else cust1 as cust1 end, CASE cust2 WHEN null then 'null' else cust1 as cust1 end, CASE cust3 WHEN null then 'null' else cust1 as cust1 end, CASE cust4 WHEN null then 'null' else cust1 as cust1 end, CASE cust5 WHEN null then 'null' else cust1 as cust1 end, CASE cust6 WHEN null then 'null' else cust1 as cust1 end 来自 foo ;

Answer 3

As per below query , I able to get not null columns at row-level col1,col3 and col4.

Query :
select 'col1' as "Name",col1 from temp
 where  exists (select  1 
 from temp
 group by to_char(col1)
 having (count(to_char(col1)))> 0)
 union all 
 select 'col2' as "Name",to_char(col2) from temp
 where  exists (select  1 
 from temp
 group by to_char(col2)
 having (count(to_char(col2)))> 0)
 union all
 select 'col3' as "Name" , to_char(col3) from temp
 where  exists (select  1 
 from temp
 group by to_char(col3)
 having (count(to_char(col3)))> 0)
 union all
 select 'col4'as "Name" , to_char(col4) from temp
 where  exists (select  1 
 from temp
 group by to_char(col4)
 having (count(to_char(col4)))> 0)
 union all
 select 'col5' as "Name" , to_char(col5) from temp
 where  exists (select  1 
 from temp
 group by to_char(col5)
 having (count(to_char(col5)))> 0)
 union all
 select 'col6' as "Name" , to_char(col6) from temp
 where  exists (select  1 
 from temp
 group by to_char(col6)
 having (count(to_char(col6)))> 0)

output:

col1    A
col1    B
col1    C
col1    D
col3    10
col3    20
col3     - 
col3    10
col4    12
col4    23
col4    34
col4    43

I tried to make this output of rows to columns but I couldn't make it in single query ... Hope this will be helpful ... 

Answer 4

我通常会分三个步骤完成此操作。

首先，确保表格统计信息是最新的。检查last_analyzed 是否晚于对表格的最后一次更改。

SELECT last_analyzed FROM user_tables WHERE table_name = 'MYTABLE';

如有疑问，请更新统计信息

BEGIN dbms_stats.gather_table_stats('MYSCHEMA','MYTABLE'); END;
/

现在，视图user_tab_columns 有一个列num_nulls。这是此列为NULL 的行数。如果该值与表中的行数相同，则所有行都是NULL。这可用于让 Oracle 生成所需的 SQL：

WITH 
  qtab AS (SELECT owner, table_name, num_rows
             FROM all_tables 
            WHERE owner='SCOTT'            -- change to your schema
              AND table_name='EMPLOYEES'   -- change to your table name
           ),
  qcol AS (SELECT owner, table_name, column_name, column_id
             FROM qtab t 
             JOIN all_tab_columns c USING (owner, table_name)
            WHERE c.nullable = 'N'         -- protected by NOT NULL constraint 
               OR c.num_nulls = 0          -- never NULL
               OR c.num_nulls < t.num_rows -- at least 1 row is NOT NULL
              )  
              )  
SELECT 'SELECT '||LISTAGG(column_name,',') WITHIN GROUP (ORDER BY column_id)||
        ' FROM '||owner||'.'||table_name||';' AS my_query
  FROM qcol
 GROUP BY owner, table_name;

这将输出类似

的查询

SELECT col1, col3, col4, col5 FROM myschema.mytable;

现在可以执行此查询以显示列值。