SQL & PL/SQL

Hi,

Could you please let me know if "Count(Distinct Case" statement is efficient for a million rows or is there a better way to do it

For example -this table below contains a set of customers with status flag as 'new' or 'existing'.


CREATE TABLE tableA
( cust_id NUMBER
, status VARCHAR(10)
,txn_id NUMBER
);

INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 6433, 'New', 11);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 6433, 'New', 21);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 1234, 'existing', 31);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 1234, 'existing', 41);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 7654, 'New', 51);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 7654, 'New', 61);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 9999, 'existing', 71);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 8888, 'New', 81);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 8888, 'existing', 91);
INSERT INTO tableA (cust_id, status,txn_id) VALUES ( 2121, 'New', 100);

am using the below SQL to calculate the number of distinct customers with status 'New'.

Select
Count(Distinct Case When status = 'New' Then cust_id end) New_Cust_Cnt
from tableA

Regards
-Learnsequel