How to Use Count() and Distinct Together

Can I use COUNT() and DISTINCT together?

Sure.

SELECT COUNT(DISTINCT column) FROM table;

Selecting COUNT(*) with DISTINCT

Count all the DISTINCT program names by program type and push number

SELECT COUNT(DISTINCT program_name) AS Count,
  program_type AS [Type] 
FROM cm_production 
WHERE push_number=@push_number 
GROUP BY program_type

DISTINCT COUNT(*) will return a row for each unique count. What you want is COUNT(DISTINCT <expression>): evaluates expression for each row in a group and returns the number of unique, non-null values.

Using DISTINCT and COUNT together in a MySQL Query

use

SELECT COUNT(DISTINCT productId) from  table_name WHERE keyword='$keyword'

Counting DISTINCT over multiple columns

If you are trying to improve performance, you could try creating a persisted computed column on either a hash or concatenated value of the two columns.

Once it is persisted, provided the column is deterministic and you are using "sane" database settings, it can be indexed and / or statistics can be created on it.

I believe a distinct count of the computed column would be equivalent to your query.

SQL Server how can I use COUNT DISTINCT(*) in HAVING clause?

You probably want SELECT COUNT(DISTINCT orderid) instead of DISTINCT COUNT(customerid):

USE MyCompany;
GO
SELECT COUNT(DISTINCT orderid) AS NumberOfOrdersMade, customerid AS
CustomerID
FROM tblItems_Ordered
GROUP BY customerid
HAVING COUNT(DISTINCT orderid) > 1
GO

When outside of the COUNT, the DISTINCT will eliminate duplicate rows from a result set, which will have no effect in your query because you are doing a GROUP BY. When inside the COUNT, DISTINCT will limit the count to unique values of the column that you pass to the count function. Thus, it makes more sense to use an orderid column instead of customerid when you're aliasing it as NumberOfOrdersMade.

how to use count and distinct together

You can use distinct inside count:

select count(distinct country)
from customers;

Which is equivalent to:

select count(*)
from (  
  select distinct country
  from customers
  where country is not null
) t;

COUNT DISTINCT with CONDITIONS

You can try this:

select
  count(distinct tag) as tag_count,
  count(distinct (case when entryId > 0 then tag end)) as positive_tag_count
from
  your_table_name;

The first count(distinct...) is easy.
The second one, looks somewhat complex, is actually the same as the first one, except that you use case...when clause. In the case...when clause, you filter only positive values. Zeros or negative values would be evaluated as null and won't be included in count.

One thing to note here is that this can be done by reading the table once. When it seems that you have to read the same table twice or more, it can actually be done by reading once, in most of the time. As a result, it will finish the task a lot faster with less I/O.

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