1SELECT COUNT(*) FROM my_table;
2SELECT COUNT(*) FROM my_table WHERE my_column IS NULL;
3SELECT COUNT(*) FROM my_table WHERE my_column = 'my_value';
4SELECT COUNT(DISTINCT tel) gender_count,
5 COUNT(DISTINCT CASE WHEN gender = 'male' THEN tel END) male_count,
6 COUNT(DISTINCT CASE WHEN gender = 'female' THEN tel END) female_count
7FROM people;