DROP DATABASE IF EXISTS mcs190_db;
CREATE DATABASE mcs190_db;
USE mcs190_db;
CREATE TABLE t1 (a INT, b CHAR(5))ENGINE=Columnstore;
INSERT INTO t1 VALUES (NULL, ''),(1, 'aaa'),(2, 'aaa'),(1, 'ccc'),(4, 'ddd'),(5, 'aaa'),(6, 'ddd'),(7, 'eee');
SELECT MAX(DISTINCT a) FROM t1;
MAX(DISTINCT a)
7
SELECT MAX(DISTINCT a) FROM t1 GROUP BY b HAVING b = 'aaa';
MAX(DISTINCT a)
5
SELECT b, MAX(DISTINCT a) FROM t1 GROUP BY b ORDER BY b DESC;
b	MAX(DISTINCT a)
eee	7
ddd	6
ccc	1
aaa	5
NULL	NULL
SELECT MAX(a) FROM t1;
MAX(a)
7
DROP DATABASE mcs190_db;