Return 1 or 0 as a subquery field with EXISTS? - sql

I'm struggling to figure this one out.
What I want to do is like so:
select [fields],
((select <criteria>) return 0 if no rows returned, return 1 if any rows returned) as SubqueryResult
where a=b
Is this possible?


Please try:
select [fields],
case when (select COUNT(*) from YourTable with criteria)>0 then
1
else
0
end
as SubqueryResult
where a=b


In T-sql you can use Exists clause for the given requirement as:
select [fields],
case when exists (select <criteria> from <tablename> ) then 1
else 0
end as SubqueryResult
from <tablename>
where a=b


Also in TSQL you can do it using ISNULL() and SELECT TOP 1:
select [fields],
ISNULL((SELECT TOP 1 1 FROM YourTable WHERE <criteria> ),0)
as SubqueryResult
where a=b

Related

CASE or IF statement in WHERE clause

How can I use CASE statement or IF statement in WHERE clause ?
I am trying to apply a check on the basis of COUNT
SELECT * FROM sometable
WHERE CASE WHEN (SELECT COUNT(*) FROM sometable s WHERE SP = 2 AND sometable.id = s.id) > 2 THEN sometable.SP IS NOT NULL END
So basically if the count of rows is more than 1 it should apply IS NOT NULL condition else it should not.

Your logic suggests something like:
SELECT s.*
FROM (SELECT s.*,
SUM(CASE WHEN sp = 2 THEN 1 ELSE 0 END) OVER (PARTITION BY id) as cnt_2
FROM sometable s
) s
WHERE cnt_2 <= 2 OR s.sp is not null;
That seems equivalent. The logic doesn't seem particularly useful though.

MSSQL Return 0 for null blank

select COALESCE([ItemSlotX],0) as [ItemSlotX],COALESCE([ItemSlotY], 0 ) as [ItemSlotY] from [PowerUP_Items] where [ItemIndex]=16 and [ItemGroup]=255
In my case, is no record.
How can I return 0 for ItemSlotX and 0 for ItemSlotY if there is no record found?

If you want the results, even when there is no matching row, use this:
select COALESCE([ItemSlotX],0) as [ItemSlotX],COALESCE([ItemSlotY], 0 ) as [ItemSlotY]
from (select null dummy ) d
left
outer
join [PowerUP_Items]
on [ItemIndex]=16 and [ItemGroup]=255

This?
select ItemSlotX, ItemSlotY from PowerUP_Items where ItemIndex=16 and ItemGroup=255
if ##rowcount = 0
select 0 as ItemSlotX, 0 as ItemSlotY
Or more general approach:
if exists (select * from PowerUP_Items where ItemIndex=16 and ItemGroup=255)
select ItemSlotX, ItemSlotY from PowerUP_Items where ItemIndex=16 and ItemGroup=255
else
select 0 as ItemSlotX, 0 as ItemSlotY

If your query must return not more than one row, try this
select COALESCE(max([ItemSlotX]),0) as [ItemSlotX],COALESCE(max([ItemSlotY]), 0 ) as [ItemSlotY]
from [PowerUP_Items] where [ItemIndex]=16 and [ItemGroup]=255

Select Records from First OR occurence within a multiple AND/OR T-SQL statement within a function

I have the following SQL (example):
SET #Return_Value = = (SELECT Top 1
(CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END)
FROM TableA WHERE (Lots of AND Statements)
AND
(
(bla1)
OR
(bla2)
OR
(bla3)
)
The bla1, etc are logic to retrieve colum values from TableA. How can I return the values from bla1 if they were found without executing bla2 or bla3 because those might overwrite what I'm looking for? In other words I only want to execute OR statements if the previous one didn't find data, all this within a function.

You can use a case expression as :
SET #Return_Value = (SELECT Top 1
(CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END)
FROM TableA WHERE (Lots of AND Statements)
AND
( 1 = case when condition1 then 1
case when condition2 then 1
case when condition3 then 1
end
);

you can use order by, like
select Top 1
CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END
FROM TableA
WHERE
(Lots of AND Statements) AND
(
(bla1) OR
(bla2) OR
(bla3)
)
order by
case
when (bla1) then 1
when (bla2) then 2
when (bla3) then 3
else 999
end
Or you can try to simplify it (but you have to check performance):
select Top 1
CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END
FROM TableA
outer apply (
select
case
when (bla1) then 1
when (bla2) then 2
when (bla3) then 3
end as T
) as C
WHERE
(Lots of AND Statements) and
C.T is not null
order by C.T
or, for example, you can use union, something like this:
with cte as (
select Top 1
CASE WHEN .... THEN ColumValue1 ELSE ColumValue2 END as data
FROM TableA
WHERE
(Lots of AND Statements)
), cte2 as (
select top 1 data, 1 as c from cte where (bla1)
union all
select top 1 data, 2 as c from cte where (bla2)
union all
select top 1 data, 3 as c from cte where (bla3)
)
select top 1 data
from cte2
order by c

How to use Select Exists in Oracle?

What is the equivalent of the below SQL Query in Oracle?
SELECT CAST(
CASE WHEN EXISTS(SELECT * FROM theTable where theColumn like 'theValue%') THEN 1
ELSE 0
END
AS BIT)
I just want an oracle query where exists is used and it returns 0 or 1 like above.

The equivalent would be:
select count(*)
from dual
where exists (SELECT * FROM theTable where theColumn like 'theValue%')

This would show the same output. Just removed the CAST and added a FROM dual as Oracle doesn't allow queries with SELECT and without FROM:
SELECT
CASE WHEN EXISTS(SELECT * FROM theTable where theColumn like 'theValue%')
THEN 1
ELSE 0
END
FROM dual ;
Tested at SQL-Fiddle

You could write it:
SELECT COUNT(*) FROM theTable WHERE theColumn LIKE 'theValue%' AND ROWNUM = 1
This will return 0-1 and the optimizer gets that the query is to be optimized for first-row access.

You could also use MAX with CASE:
SELECT MAX(
CASE
WHEN theColumn like 'theValue%' THEN 1
ELSE
0
END)
AS BIT
FROM theTable

You can use one of the following queries: (the first ones is more performant)
SELECT H.TABLE_ID, H.OTHER_FIELD,
(SELECT 'YES' FROM DUAL WHERE EXISTS (SELECT 'X' FROM TABLE_DETAIL DT
WHERE DT.TABLE_ID = H.TABLE_ID) ) WITH_DETAIL FROM TABLE_HEADER H;
SELECT H.TABLE_ID, H.OTHER_FIELD,
CASE WHEN EXISTS(SELECT * FROM IMTS.DETAIL_TABLE DT WHERE DT.TABLE_ID=H.TABLE_ID)
THEN 'Y' ELSE 'N' END WITH_DETAIL FROM HEADER_TABLE H;
SELECT H.TABLE_ID, H.OTHER_FIELD, NVL2(DT.SOME_NOTNULL_FIELD, 'YES','NO') WITH_DETAIL
FROM TABLE_HEADER H
LEFT JOIN TABLE_DETAIL DT ON DT.TABLE_ID=H.TABLE_ID AND ROWNUM<2;

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;