Question

Suppose that we have a table and save on it customerid and orderid.

What is the best approach for take count of all order and check exist of certain customerid in one query ?

I know that this query is wrong but I forced write that because Stackoverflow did not allow me post short question!

For example :

(table name tbTest)

SELECT 
    COUNT(ORDERID), 
    EXIST(SELECT ID FROM tbTest WHERE customerid = {n}) 
FROM tbTest

Answer 1

Please try with the follwoing

SELECT  COUNT(ORDERID),
        CASE
            WHEN EXISTS(SELECT ID FROM tbTest WHERE customerid = {n}) then 'Exist'  
            ELSE 'Not Exist'
        END
FROM tbTest