在单个查询中计算空值和非空值

我有桌子

create table us
(
 a number
);

现在我有类似的数据：

a
1
2
3
4
null
null
null
8
9

现在，我需要一个查询来计算a列中的空值和非空值

这适用于Oracle和SQL Server（您可能可以使其在另一个RDBMS上运行）：

select sum(case when a is null then 1 else 0 end) count_nulls
     , count(a) count_not_nulls 
  from us;

要么：

select count(*) - count(a), count(a) from us;

如果我理解正确的话，您想在一列中计算所有NULL和所有NOT NULL。

如果正确的话：

SELECT count(*) FROM us WHERE a IS NULL 
UNION ALL
SELECT count(*) FROM us WHERE a IS NOT NULL

阅读评论后，可进行完整查询：]

SELECT COUNT(*), 'null_tally' AS narrative 
  FROM us 
 WHERE a IS NULL 
UNION
SELECT COUNT(*), 'not_null_tally' AS narrative 
  FROM us 
 WHERE a IS NOT NULL;

这是适用于Oracle的快速而肮脏的版本：

select sum(case a when null then 1 else 0) "Null values",
       sum(case a when null then 0 else 1) "Non-null values"
from us

据我了解您的查询，您只需运行此脚本并获得Total Null，Total NotNull行，

select count(*) - count(a) as 'Null', count(a) as 'Not Null' from us;

非空

select count(a)
from us

为空

select count(*)
from us

minus 

select count(a)
from us

因此

SELECT COUNT(A) NOT_NULLS
FROM US

UNION

SELECT COUNT(*) - COUNT(A) NULLS
FROM US

应该做的工作

更好的是，列标题正确显示。

SELECT COUNT(A) NOT_NULL, COUNT(*) - COUNT(A) NULLS
FROM US

在我的系统上进行的一些测试中，它需要进行全表扫描。

通常我用这个把戏

select sum(case when a is null then 0 else 1 end) as count_notnull,
       sum(case when a is null then 1 else 0 end) as count_null
from tab
group by a

为了提供另一种选择，Postgres 9.4+ 允许将a FILTER应用于聚合：

SELECT
  COUNT(*) FILTER (WHERE a IS NULL) count_nulls,
  COUNT(*) FILTER (WHERE a IS NOT NULL) count_not_nulls
FROM us;

SQLFiddle：http ://sqlfiddle.com/#!17/80a24/5

这有点棘手。假设表只有一列，则Count（1）和Count（*）将给出不同的值。

set nocount on
    declare @table1 table (empid int)
    insert @table1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(NULL),(11),(12),(NULL),(13),(14);

    select * from @table1
    select COUNT(1) as "COUNT(1)" from @table1
    select COUNT(empid) "Count(empid)" from @table1

查询结果

如您在图像中看到的，第一个结果显示该表有16行。其中两行为NULL。因此，当我们使用Count（*）时，查询引擎将对行数进行计数，因此我们得到的计数结果为16。但是在Count（empid）的情况下，它会计算empid列中的非NULL值。所以我们得到的结果是14。

因此，每当使用COUNT（Column）时，请确保我们处理NULL值，如下所示。

select COUNT(isnull(empid,1)) from @table1

将同时计数NULL和Non-NULL值。

注意：即使表由多个列组成，也是如此。Count（1）将给出总行数，而与NULL / Non-NULL值无关。仅当使用Count（Column）对列值进行计数时，我们才需要注意NULL值。

我有一个类似的问题：计算所有不同的值，将空值也计算为1。在这种情况下，简单的计数不起作用，因为它不考虑空值。

这是一个适用于SQL且不涉及选择新值的代码段。基本上，一旦执行了非重复操作，还可以使用row_number（）函数在新列（n）中返回行号，然后对该列执行计数：

SELECT COUNT(n)
FROM (
    SELECT *, row_number() OVER (ORDER BY [MyColumn] ASC) n
    FROM (
        SELECT DISTINCT [MyColumn]
                    FROM [MyTable]
        ) items  
) distinctItems

这是两个解决方案：

Select count(columnname) as countofNotNulls, count(isnull(columnname,1))-count(columnname) AS Countofnulls from table name

要么

Select count(columnname) as countofNotNulls, count(*)-count(columnname) AS Countofnulls from table name

尝试

SELECT 
   SUM(ISNULL(a)) AS all_null,
   SUM(!ISNULL(a)) AS all_not_null
FROM us;

简单！

试试这个..

SELECT CASE 
         WHEN a IS NULL THEN 'Null' 
         ELSE 'Not Null' 
       END a, 
       Count(1) 
FROM   us 
GROUP  BY CASE 
            WHEN a IS NULL THEN 'Null' 
            ELSE 'Not Null' 
          END 

如果您使用的是MS Sql Server ...

SELECT COUNT(0) AS 'Null_ColumnA_Records',
(
    SELECT COUNT(0)
    FROM your_table
    WHERE ColumnA IS NOT NULL
) AS 'NOT_Null_ColumnA_Records'
FROM your_table
WHERE ColumnA IS NULL;

我不建议您这样做...但是在这里（与结果在同一张表中）

使用ISNULL嵌入式函数。

如果是mysql，则可以尝试这样的操作。

select 
   (select count(*) from TABLENAME WHERE a = 'null') as total_null, 
   (select count(*) from TABLENAME WHERE a != 'null') as total_not_null
FROM TABLENAME

SELECT SUM(NULLs) AS 'NULLS', SUM(NOTNULLs) AS 'NOTNULLs' FROM 
    (select count(*) AS 'NULLs', 0 as 'NOTNULLs' FROM us WHERE a is null
    UNION select 0 as 'NULLs', count(*) AS 'NOTNULLs' FROM us WHERE a is not null) AS x

这很麻烦，但它会返回一条带有2个列的记录，指示空值与非空值的计数。

这在T-SQL中有效。如果您只是在计算某件商品的数量，并且想要包含空值，请使用COALESCE代替大小写。

IF OBJECT_ID('tempdb..#us') IS NOT NULL
    DROP TABLE #us

CREATE TABLE #us
    (
    a INT NULL
    );

INSERT INTO #us VALUES (1),(2),(3),(4),(NULL),(NULL),(NULL),(8),(9)

SELECT * FROM #us

SELECT CASE WHEN a IS NULL THEN 'NULL' ELSE 'NON-NULL' END AS 'NULL?',
        COUNT(CASE WHEN a IS NULL THEN 'NULL' ELSE 'NON-NULL' END) AS 'Count'
    FROM #us
    GROUP BY CASE WHEN a IS NULL THEN 'NULL' ELSE 'NON-NULL' END

SELECT COALESCE(CAST(a AS NVARCHAR),'NULL') AS a,
        COUNT(COALESCE(CAST(a AS NVARCHAR),'NULL')) AS 'Count'
    FROM #us
    GROUP BY COALESCE(CAST(a AS NVARCHAR),'NULL')

在Alberto的基础上，我添加了汇总。

 SELECT [Narrative] = CASE 
 WHEN [Narrative] IS NULL THEN 'count_total' ELSE    [Narrative] END
,[Count]=SUM([Count]) FROM (SELECT COUNT(*) [Count], 'count_nulls' AS [Narrative]  
FROM [CrmDW].[CRM].[User]  
WHERE [EmployeeID] IS NULL 
UNION
SELECT COUNT(*), 'count_not_nulls ' AS narrative 
FROM [CrmDW].[CRM].[User] 
WHERE [EmployeeID] IS NOT NULL) S 
GROUP BY [Narrative] WITH CUBE;

SELECT
    ALL_VALUES
    ,COUNT(ALL_VALUES)
FROM(
        SELECT 
        NVL2(A,'NOT NULL','NULL') AS ALL_VALUES 
        ,NVL(A,0)
        FROM US
)
GROUP BY ALL_VALUES

select count(isnull(NullableColumn,-1))

所有答案都是错误的或过时的。

执行此查询的简单正确方法是使用COUNT_IFfunction。

SELECT
  COUNT_IF(a IS NULL) AS nulls,
  COUNT_IF(a IS NOT NULL) AS not_nulls
FROM
  us

以防万一您希望在单个记录中使用它：

select 
  (select count(*) from tbl where colName is null) Nulls,
  (select count(*) from tbl where colName is not null) NonNulls 

;-)

用于计算非空值

select count(*) from us where a is not null;

用于计数空值

 select count(*) from us where a is null;

我在postgres 10中创建了表格，以下两项均有效：

select count(*) from us

和

select count(a is null) from us

就我而言，我希望在多个列之间使用“ 空分布 ”：

SELECT
       (CASE WHEN a IS NULL THEN 'NULL' ELSE 'NOT-NULL' END) AS a_null,
       (CASE WHEN b IS NULL THEN 'NULL' ELSE 'NOT-NULL' END) AS b_null,
       (CASE WHEN c IS NULL THEN 'NULL' ELSE 'NOT-NULL' END) AS c_null,
       ...
       count(*)
FROM us
GROUP BY 1, 2, 3,...
ORDER BY 1, 2, 3,...

按照“ ...”，它可以轻松扩展到更多列，并根据需要扩展

a为空的元素数：

select count(a) from us where a is null;

a不为null的元素数：

select count(a) from us where a is not null;