replace some value in sql with Null and perform count function in sql server while performing group by - sql

there is LAT_LONG field which I want to count for each ID, the LAT_LONG contain some string value as 'null/null' which I want to replace with NULL, and than perform the group by operation
select ID, COUNT(LAT_LONG) as LAT_LONG_CAT from mytable group by ID
How to replace 'null/null' string with Null in LAT_LONG field


In SQL Server you can simply use NULLIF function like so:
SELECT lat_long, NULLIF(lat_long, 'null/null') AS lat_long_parsed FROM mytable
Example on dbfiddle
So in the end your query would be:
SELECT ID
, COUNT(NULLIF(lat_long, 'null/null')) AS LAT_LONG_CAT
FROM mytable
GROUP BY id


Use a CASE expression:
SELECT ID,
COUNT(CASE WHEN LAT_LONG <> 'null/null'
THEN LAT_LONG END) AS LAT_LONG_CNT
FROM mytable
GROUP BY ID;
The above CASE expression will treat a value of null/null as NULL, otherwise it counts the LAT_LONG field directly.

Related

BigQuery(standard SQL) grouping values based on first CASE WHEN statement

Here is my query with the output below the syntax.
SELECT DISTINCT CASE WHEN id = 'RUS0261431' THEN value END AS sr_type,
COUNT(CASE WHEN id in ('RUS0290788') AND value in ('1','2','3','4') THEN respondentid END) AS sub_ces,
COUNT(CASE WHEN id IN ('RUS0290788') AND value in ('5','6','7') THEN respondentid END) AS pos_ces,
COUNT(*) as total_ces
FROM `some_table`
WHERE id in ( 'RUS0261431') AND id <> '' AND value IS NOT NULL
GROUP BY 1
As you can see with the attached table I'm unable to group the values based on Id RUS0290788 with the distinct values that map to RUS0261431. Is there anyway to pivot with altering my case when statements so I can group sub_ces and pos_ces by sr_type. Thanks in advanceenter image description here

You can simplify your WHERE condition to WHERE id = ('RUS0261431'). Only records with this value will be selected so you do not have to repeat this in the CASE statements.

Not a group expression: troubleshooting an Oracle query

Oracle query
I have a column value with hardcoded value 'N/A' and other char values as well. I need to write a select query to get the min of this column grouping the other set of columns.. but the challenge is i need to replace the hard coded value of 'N/A' with another character 'Abc' along with min function
Option 1: nvl won't work as the value is hardcoded
Option 2: decode in the select statement along with min clause in the decode list, and group by clause with the other columns used in the select list
However, getting an error
ORA-00979 : not a group expression.
Example :
Select a, b, decode(z,'N/A','abc',min(z))
From table 1, table 2
Where table 1.p=table2.q
Group by a,b
Having c.table1 >= table2.d

You should be using DECODE inside the MIN function, not the other way around. But, I would probably just use a single CASE expression here:
SELECT
a,
b,
MIN(CASE WHEN z = 'N/A' THEN 'abc' ELSE z END) AS min_value
FROM table1 t1
INNER JOIN table2 t2
ON t1.p = t2.q
GROUP BY
a,
b;
The above CASE expression is just taking the minimum value of z for each group, with the only difference between MIN(z) being that should the value be N/A, it would be treated as abc.

Showing sum of conditions as one row

Hi I have a table like this
select id, value, condition from mytable
result
and I need a query to make it like this
is it possible?

Just use conditional aggregation:
select id,
sum(case when condition = 'true' then value else 0 end) as num_true,
sum(case when condition = 'false' then value else 0 end) as num_false
from t
group by id;
You have tagged the question with both Oracle and SQL Server. Neither supports a boolean type directly in SQL, so I am guessing that the condition is a string.

yes possible
select id "id", sum(decode(condition,'TRUE',value,0)) "sum_of_condition_true",
sum(decode(condition,'FALSE',value,0)) "sum_of_condition_false"
from mytable
group by id
order by id;

Referring to results of a sub query in main query

I have a sub query that returns one column, showing as GroupType, I then want to do a CASE function on this result within the main query, however I get an invalid column name when using the CASE statement.
Can i do this in SQL to do I have to refer to it by a different name

SELECT CASE
WHEN
(
SELECT column
FROM othertable
) = 1
THEN '1'
ELSE '2'
END
FROM mytable
To reuse the subquery result:
SELECT subvalue, CASE subvalue WHEN 1 THEN 1 ELSE 2 END
FROM (
SELECT (
SELECT column
FROM othertable
) AS subvalue
FROM mytable
) q

Counting null and non-null values in a single query

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;