Suppose I have a table named "Expense" and it has some month-wise expense which may contain some "NULL", now I want to check the yearly expenses in total with this below query:-
Select Sum(January) + Sum (February) ..... (I skipped the rest 10 months)
from Expense
This gives result as "NULL"
How can I avoid this situation? I think there are more convenient way to check the yearly sum
All arithmetic or logical operations involving NULL yield NULL. For example:
SELECT 1 + NULL -- NULL
You must convert NULL to zeros before you can + them:
SELECT
COALESCE(SUM(January), 0) +
COALESCE(SUM(February) , 0) +
...
It is also possible to add the columns first and then calculate the sum:
SELECT SUM(
COALESCE(January, 0) +
COALESCE(February, 0) +
)
Be advised that (i) SUM skips NULL values (ii) returns NULL instead of 0 if all values are NULL:
SELECT SUM(a) FROM (VALUES
(1),
(2),
(NULL)
) AS v(a) -- returns 3 instead of NULL
It will return NULL if all values encountered were NULL:
SELECT SUM(a) FROM (VALUES
(CAST(NULL AS INT)),
(NULL),
(NULL)
) AS v(a) -- returns NULL instead of 0
use coalesce function to convert null to 0 then use sum
Select Sum(coalesce(January,0)) + Sum (coalesce(February,0)) ..... (I skipped the rest 10 months)
from Expense
Just use coalesce [ with 0 as the second argument ] to replace nulls for all month columns, otherwise you can not get true results from aggregation of numeric values :
select sum(coalesce(January,0)+coalesce(February,0) ... )
from Expense
That because you have NULL values, you can use Case, Coalesce or IIF:
Select SUM(IIF(Col IS NULL, 0, Col))
Select SUM(CASE WHEN Col IS NULL THEN 0 ELSE Col END)
Select COALESCE(Sum(Col), 0)
Any arithmetic function will return null if there is at least one null value in the given column. That's why you should use functions like coalesce or isNull (MSSQL), NVL (Oracle).
You can use ISNULL(SUM(January),0).
Because null + value is always null and in your sample some months sums are null, you can avoid this by adding ISNULL
Select isnull(Sum(January),0) +
isnull(Sum(February),0)
--..... (I skipped the rest 10 months)
from Expense
Alternatively you can use below way:
Select Sum(
isnull(January,0) +
isnull(February,0)
)
--..... (I skipped the rest 10 months)
from Expense
I'm trying to select the last enddate per nr. In case the nr contains an enddate with value NULL, it means this nr is still active. In short I cannot use MAX(enddate) because out of 2013-09-25 and NULL it would select the date whereas I need NULL.
I tried the following query though it seems that NULL IN (enddate) does not return what I suspected. Namely: 'if the array contains at least one value NULL...'. In other words, NULL should overrank MAX().
SELECT nr,
CASE WHEN NULL IN (enddate) THEN NULL ELSE MAX(enddate) END
FROM myTable
GROUP BY nr
Does someone know how to replace this expression?
You can use the query below. It returns NULL before other dates (provided that you put a date great enough) and then restores NULL.
SELECT nr, CASE d WHEN '20990101' THEN NULL ELSE d END d
FROM (
SELECT nr,
CASE MAX(ISNULL(enddate, '20990101') d
FROM myTable
GROUP BY nr
)
I couldn't check the syntax so there may be small typos.
You could use this query. The CTE calculates the maximum date ignoring any nulls, this is then left joined back to the table to see if there is a null value for each nr value. The case statement returns a null if it exists or the maximum date from the CTE.
WITH CTE1 AS
(SELECT nr, MAX(enddate) MaxEnddate
FROM myTable
GROUP BY nr)
SELECT CTE1.nr,
CASE WHEN MyTable.enddate IS NULL AND MyTable.NR IS NOT NULL THEN NULL ELSE CTE1.MaxEndDate END AS EndDate
FROM CTE1
LEFT JOIN MyTable
ON MyTable.nr=CTE1.nr
AND MyTable.enddate IS NULL
Just to build off of #Szymon answer a little bit:
drop table #temp
create table #temp (MyDate date) insert into #temp (MyDate) values ('1/1/2010'),('1/1/2011'),('1/1/2012'),(NULL)
select * from #temp
SELECT
(CASE WHEN MAX(ISNULL(MyDate, '2099-01-01')) = '2099-01-01' THEN NULL ELSE MAX(ISNULL(MyDate, '2099-01-01')) END) as Max_Date
FROM
#temp
The query replaces a NULL value with '2099-01-01'. Then, it looks to see if the Max is equal to '2099-01-01' and if so, returns NULL, and otherwise returns the actual Max.
I have a table
create table us
(
a number
);
Now I have data like:
a
1
2
3
4
null
null
null
8
9
Now I need a single query to count null and not null values in column a
This works for Oracle and SQL Server (you might be able to get it to work on another RDBMS):
select sum(case when a is null then 1 else 0 end) count_nulls
, count(a) count_not_nulls
from us;
Or:
select count(*) - count(a), count(a) from us;
If I understood correctly you want to count all NULL and all NOT NULL in a column...
If that is correct:
SELECT count(*) FROM us WHERE a IS NULL
UNION ALL
SELECT count(*) FROM us WHERE a IS NOT NULL
Edited to have the full query, after reading the comments :]
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;
Here is a quick and dirty version that works on Oracle :
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
for non nulls
select count(a)
from us
for nulls
select count(*)
from us
minus
select count(a)
from us
Hence
SELECT COUNT(A) NOT_NULLS
FROM US
UNION
SELECT COUNT(*) - COUNT(A) NULLS
FROM US
ought to do the job
Better in that the column titles come out correct.
SELECT COUNT(A) NOT_NULL, COUNT(*) - COUNT(A) NULLS
FROM US
In some testing on my system, it costs a full table scan.
As i understood your query, You just run this script and get Total Null,Total NotNull rows,
select count(*) - count(a) as 'Null', count(a) as 'Not Null' from us;
usually i use this trick
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
Just to provide yet another alternative, Postgres 9.4+ allows applying a FILTER to aggregates:
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
This is little tricky. Assume the table has just one column, then the Count(1) and Count(*) will give different values.
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
Query Results
As you can see in the image, The first result shows the table has 16 rows. out of which two rows are NULL. So when we use Count(*) the query engine counts the number of rows, So we got count result as 16. But in case of Count(empid) it counted the non-NULL-values in the column empid. So we got the result as 14.
so whenever we are using COUNT(Column) make sure we take care of NULL values as shown below.
select COUNT(isnull(empid,1)) from #table1
will count both NULL and Non-NULL values.
Note: Same thing applies even when the table is made up of more than one column. Count(1) will give total number of rows irrespective of NULL/Non-NULL values. Only when the column values are counted using Count(Column) we need to take care of NULL values.
I had a similar issue: to count all distinct values, counting null values as 1, too. A simple count doesn't work in this case, as it does not take null values into account.
Here's a snippet that works on SQL and does not involve selection of new values.
Basically, once performed the distinct, also return the row number in a new column (n) using the row_number() function, then perform a count on that column:
SELECT COUNT(n)
FROM (
SELECT *, row_number() OVER (ORDER BY [MyColumn] ASC) n
FROM (
SELECT DISTINCT [MyColumn]
FROM [MyTable]
) items
) distinctItems
Try this..
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
Here are two solutions:
Select count(columnname) as countofNotNulls, count(isnull(columnname,1))-count(columnname) AS Countofnulls from table name
OR
Select count(columnname) as countofNotNulls, count(*)-count(columnname) AS Countofnulls from table name
Try
SELECT
SUM(ISNULL(a)) AS all_null,
SUM(!ISNULL(a)) AS all_not_null
FROM us;
Simple!
If you're using 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;
I don't recomend you doing this... but here you have it (in the same table as result)
use ISNULL embedded function.
All the answers are either wrong or extremely out of date.
The simple and correct way of doing this query is using COUNT_IF function.
SELECT
COUNT_IF(a IS NULL) AS nulls,
COUNT_IF(a IS NOT NULL) AS not_nulls
FROM
us
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
It's fugly, but it will return a single record with 2 cols indicating the count of nulls vs non nulls.
This works in T-SQL. If you're just counting the number of something and you want to include the nulls, use COALESCE instead of 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')
Building off of Alberto, I added the rollup.
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))
if its mysql, you can try something like this.
select
(select count(*) from TABLENAME WHERE a = 'null') as total_null,
(select count(*) from TABLENAME WHERE a != 'null') as total_not_null
FROM TABLENAME
Just in case you wanted it in a single record:
select
(select count(*) from tbl where colName is null) Nulls,
(select count(*) from tbl where colName is not null) NonNulls
;-)
for counting not null values
select count(*) from us where a is not null;
for counting null values
select count(*) from us where a is null;
I created the table in postgres 10 and both of the following worked:
select count(*) from us
and
select count(a is null) from us
In my case I wanted the "null distribution" amongst multiple columns:
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,...
As per the '...' it is easily extendable to more columns, as many as needed
Number of elements where a is null:
select count(a) from us where a is null;
Number of elements where a is not null:
select count(a) from us where a is not null;
SELECT
sum(TotalHoursM)
+ (TotalHoursT)
+ (TotalHoursW)
+ (TotalHoursTH)
+ (TotalHoursF)
AS TOTAL
FROM LeaveRequest
If the column has a 0 value, you are fine, my guess is that you have a problem with a Null value, in that case you would need to use IsNull(Column, 0) to ensure it is always 0 at minimum.
The previous answers using the ISNULL function are correct only for MS Sql Server. The COALESCE function will also work in SQL Server. But will also work in standard SQL database systems. In the given example:
SELECT sum(COALESCE(TotalHoursM,0))
+ COALESCE(TotalHoursT,0)
+ COALESCE(TotalHoursW,0)
+ COALESCE(TotalHoursTH,0)
+ COALESCE(TotalHoursF,0) AS TOTAL FROM LeaveRequest
This is identical to the ISNULL solution with the only difference being the name of the function. Both work in SQL Server but, COALESCE is ANSI standard and ISNULL is not. Also, COALESCE is more flexible.
ISNULL will only work with two parameters. If the first parameter is NULL then the value of the second parameter is returned, else the value of the first is returned.
COALESCE will take 2 to 'n' (I don't know the limit of 'n') parameters and return the value of the first parameter that is not NULL. When there are only two parameters the effect is the same as ISNULL.
SELECT sum(isnull(TotalHoursM,0))
+ isnull(TotalHoursT,0)
+ isnull(TotalHoursW,0)
+ isnull(TotalHoursTH,0)
+ isnull(TotalHoursF,0))
AS TOTAL FROM LeaveRequest
Just for reference, the equivalent statement for MySQL is: IFNull(Column,0).
This statement evaluates as the column value if not null, otherwise it is evaluated as 0.
You can use ISNULL:
ISNULL(field, VALUEINCASEOFNULL)
looks like you want to SUM all the columns (I'm not sure where "sum 3 columns" comes from), not just TotalHoursM, so try this:
SELECT
SUM( ISNULL(TotalHoursM ,0)
+ ISNULL(TotalHoursT ,0)
+ ISNULL(TotalHoursW ,0)
+ ISNULL(TotalHoursTH ,0)
+ ISNULL(TotalHoursF ,0)
) AS TOTAL
FROM LeaveRequest
You can also use nvl(Column,0)
I would try this:
select sum (case when TotalHousM is null then 0 else TotalHousM end)
+ (case when TotalHousT is null then 0 else TotalHousT end)
+ (case when TotalHousW is null then 0 else TotalHousW end)
+ (case when TotalHousTH is null then 0 else TotalHousTH end)
+ (case when TotalHousF is null then 0 else TotalHousF end)
as Total
From LeaveRequest
If you want to avoid the null value use IsNull(Column, 1)