我有一张桌子

create table us
(
 a number
);

现在我有如下数据:

a
1
2
3
4
null
null
null
8
9

现在我需要一个查询来计算列a中的空值和非空值


当前回答

为了提供另一种选择,Postgres 9.4+允许对聚合应用FILTER:

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

其他回答

Try

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

简单!

这在T-SQL中有效。如果你只是计算一些东西的数量,你想包括空值,使用COALESCE而不是case。

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')

对于非空值

select count(a)
from us

null值

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

应该做这项工作

更好的是列标题是正确的。

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,需要进行全表扫描。

如果我理解正确,你想在一个列中计数所有NULL和所有NOT NULL…

如果是正确的:

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

阅读评论后,编辑了完整的查询:]


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;

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

下面是一个适用于SQL的代码片段,不涉及选择新值。 基本上,执行distinct后,还使用row_number()函数返回新列(n)中的行号,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