How to use subquery in sql server 2008? - sql

Question

I know this question might be repeated ... But I have query like this, I have a field "Compute_CRM_State" in my table. And that field contains data like "approved,pending,cancelled" but now i want to fetch total count of approved or pending or cancelled. I tried it with sub query. I can able to get total count of approved or pending or cancelled but.. I got same records many times.
query :
SELECT (SELECT COUNT(Compute_CRM_State) AS Expr1
FROM CRM_Doctor_Request
WHERE (CRM_State_Id = 1)) AS PENDING,
(SELECT COUNT(Compute_CRM_State) AS Expr2
FROM CRM_Doctor_Request AS CRM_Doctor_Request_3
WHERE (CRM_State_Id = 2)) AS Approved,
(SELECT COUNT(Compute_CRM_State) AS Expr3
FROM CRM_Doctor_Request AS CRM_Doctor_Request_2
WHERE (CRM_State_Id = 3)) AS CANCELLED
FROM CRM_Doctor_Request AS CRM_Doctor_Request_1
There should be display only 1 record of count.. but it is getting display the number of times that number of records in table contains.

Answer 1

The reason you were not getting the total count correctly and getting many records instead, is that the COUNTs are selected as a correlated subquery, so you will got the count for each record in the table.
To fix that you have to use the aggregate function in the outer query, not from the correlated subuery. And to get those total count for each status, use the CASE expression to do this like so:
SELECT
SUM(CASE WHEN CRM_State_Id = 1 THEN 1 ELSE 0 END) AS PENDING,
SUM(CASE WHEN CRM_State_Id = 2 THEN 1 ELSE 0 END) AS Approved,
SUM(CASE WHEN CRM_State_Id = 3 THEN 1 ELSE 0 END) AS CANCELLED
FROM CRM_Doctor_Request;
SQL Fiddle Demo
Or: you can use the PIVOT table operator to do the same thing:
SELECT
[1] AS PENDING,
[2] AS Approved,
[3] AS Cancelled
FROM
(
SELECT * FROM CRM_Doctor_Request
) AS t
PIVOT
(
COUNT(Compute_CRM_State)
FOR CRM_State_Id IN([1], [2], [3])
) AS p;
Like this.